What would this take? Would I have to buy an aftermarket crank? What would it take to neutral balance a stock crank?
Any idea of Cost to do so.
What are the advantages of external balance anyway?
Looking at a torquer motor for a truck that will be used as one.
I'm putting together a 80s d250 (officially let's call it an 83, even though the cab i have is 90, bed is 91, etc but the frame and everything I have here for title and vin is from the original 83 I had)
Looking at finding an nv4500 for it, want to make a good camper puller.
Couple of steps over OEM (what used to be called) "towing/ RV" cam.
4 barrel, probably a TQ. Will have AC.
S
Neutral balance stick flywheels seem easier to find, as do neutral balance harmonic balancers, that's all, as motivation to do so
Not really interested in stroker build at this point.

You are building, essentially, a stock motor.

Use the stock flywheel, not hard to find. For the balancer, Summit lists 11 offerings, again, not hard to find.

Benefits to neutral balance? In your application, none.

pretty sure the stock 5.9 is neutrally balanced.
I added an adapter flex plate to bolt it to my 318 torque converter on a 727 and didn't need to change anything. junkyard motor that ran when I got it.
so you should be good without doing anything else to it.

Are we talking internal vs external balance ?

Should be externally balanced and require the scalloped flex plate with neutral balanced torque converter.

Not stock it isn't.

Missed the part about it being a stick? I guess flywheel and NV4500 weren't clues?

You can buy, new, magnum balanced flywheels at rock auto for not a lot of money. But being this is an "AMC" build I hesitate to cite one.

ah, poster above straightens me out.
that is the flex plate I got and I have a neutral torque converter. thought it was the engine, didn't realize it was the flex plate.

No not an AMC build. It's a 2000 model year 5.9 360 cu in magnum engine being built for an 83 d250.

Yeah

30 years ago I neutral balanced my first 360 motor, which I still have, and am glad I did.

OK, then - internal vs external - I visualize it like this:

Crankshaft is taking forces from pistons & rods trying essentially to bend it.
External balance is like hanging eccentric barbell weights at the ends of the crank, which seems to be also applying an additional bending force to compensate.
Internal balance accommodates the piston & rod forces on the crank without those eccentric weights at its ends.
That would also help maintain a more consistent wedge of oil at the main bearings.
Internal balance (IB) just seems a smoother and more accurate method of addressing rotating assembly harmonics.

Granted, this may be excessive mechanical sympathy, and there are thousands of externally-balanced street motors out there apparently doing just fine.
IB may not be in the budget, isn't strictly necessary for a low-RPM street deal, and we're talking roundabout .001" - somewhere between theory & physics, one might say.
A side bonus is it'll be easier to swap converters/flywheels, and balancers, if future modifications are likely.
Bottom line for a street motor is let the wallet, intended use, and future plans dictate.

My understanding of the task a harmonic balancer is given really has little to do with weight hanging and more to do with smoothing out the power impulses of ea cylinder firing and causing the crank to rotationally resonate back and forth as it twists, leading to failure, and where the weights are added for rotational balance is somewhat inconsequential. I maybe misinformed.
I favor neutral balance mainly for convenience, irrespective of the added cost.

Yes, I put "AMC" in quotes because much like them you are using whatever parts you can get.

Which means you really need to be more specific as to exactly what parts you are using so that the combo can go together a smoothly as possible.

I'm asking what I'm asking to help somewhat determine what parts to get...

I've looked at flywheels for this engine and of what I'd come up with so far I saw listings (think I was looking at rock auto)
They showed the same flywheel for LA as for magnum and I know that's wrong. If I had a neutral balance to start with i could use a 318 flywheel which was always internal balance and so LA/magnum is less of a question. I know an LA 360 and magnum 360 are both external balance but not the same extent. I remember when I was a teenager I put a 318 in place of a 360 with the 360s original trans and torque converter and that thing shook like crazy, I forgot who told me back then what the problem was. I pulled the starter, and the inspection plate, knocked that weight off and problem solved.
This also comes into play because I have the 360 mag that was rebuilt some years ago, a job that bad. I found a different engine for that job and kept this one. It's a fresh 30 over bore job with only a few hours of run time on it (discovered the problem when I went to change oil and it came out as a silver slurry like I've never seen before) there were a couple of problems with that build,
I understand what and why it went bad, but I'm gonna go thru it again for another truck, send it back thru the machine shop for a hot tank and start fresh.
My son happens to have a set of pistons taken out of an LA 360 with only 6k miles because he wanted a 408. These are speed pro flat tops also 30 over, I believe they're h814 CP but don't quote me on that. Whatever the number is for their LA 260 flat tops is, that's what they are
I was *thinking " about trying to utilize those as they are just collecting dust otherwise, and I don't know where the imbalance difference is between an LA or magnum. If I were to revert to neutral balance that difference between the 2 versions would be null and void. I have the whole rotating assembly out of that '76 360, I guess I could build it as an LA just using the magnum block ... That may be a crazy Idea as well.

That's why I was asking what's so good about external balance anyway.... Being that 273-318-340 and 360 were part of the same engine family, I never got the reason why they weren't all either internal or external balance among them.
I have been wanting to try a set of KB (107?) in an engine too. I wasn't sure it was gonna be "this" one though.

Usually when asking questions I assume, hope, wonder that I'm not the only one wondering about what I ask....
"Bench racing", fundamentals review, whatever you want to call it.

This stuff isn't free or cheap, there's way more choices in how to build a given engine than we used to have, obviously "if it's posted on the Internet it must be true" really isn't, and all of that stuff. The process of disassembly and reassembly hasn't changed, since I started playing with cars and trucks (at least within the era I'd rather be working on) but parts choices have.

I dont mind doing one after another but I hate redo's on the same one, don't like spending twice on the same unit, not wanting bragging rights pertaining to spending either the most or the least on a given project, but more than anything I want the best bang for the buck in everything I do... And have a bunch of stuff laying around from over the many years I've been doing this ... So, hopefully can use up some of that so that I can exercise some of that bang for the buck.... But I realize that ain't always possible and is part of the reason why I have laying around "what" I have laying around at this point.

An internal balance is likely going to need Mallory metal, read expensive. Find a flywheel that will match the clutch, bellhousing, trans and engine as best as possible. Sounds like a late 90s magnum should work and match the 4500 trans and engine.

Worst case, or almost ideal depending on pov, have the flywheel balanced with the rest of the guts.

This is a great website. It should have all the info you're looking for.

https://www.magnumswap.com/

There's something to that... I've replaced many clutches over the years and never had to have anything rebalanced as a result. Just exactly what all components would have to be taken in for a balance job?
I've dealt with several machine shops over the years, all but 2 of those no longer exist.
I've never had any of these say anything about whether they offer engine balancing or suggested I might need it done to whatever I was working on at any given time.
If I was gonna have this thing balanced I have no idea who in the south suburbs of Chicago that could do so for me. Even if I extend the area to include Bloomington IL, Champaign, or Peoria I have no idea who might offer it.
Any suggestions

I would never build one without doing that, except for maybe a stone stock build. Eliminates the hassle of sourcing dampers, flexplates, all of it.

3 pieces of mallory in the last one. Stock crank. 7400 all day long.

Motor balance doesn't usually make much difference until the rpm reaches the past the 4,000 rpm range. Once it passes that 4,000 rpm range, the higher the rpm, the more critical the balance becomes.
Back in the mid 60s, few motors exceeded that 4,000 rpm range, so unless the balance was way off, it didn't make much difference. Chrysler put forth some effort in maintaining balance of the pistons in each motor, and the balance of each rod in the motor, which gave them motors that often exceeded that 100K miles range and provided adequate balance up into the 5,000 rpm range.
Chrysler was producing the 318 the 383, and the 413 as the standard motor base, then added a 426 wedge, then the 426 Hemi and a 440 and a 340 performance motors in the mid 60s. As the performance increased, Chrysler stepped up its game with motor balance. The Magnum motors (which were their performance motors) at that time were more carefully monitored performance based motors held to tighter clearances and balance the regular production motors.
By the late 60s, Chrysler saw the challenge the emission standards were going to place on their work horse basic motors, especially the 318 and the 383 were the most common work horse motors in the fleet. A 360 was developed as the next step up from the 318 as a work horse, was was basically a slightly larger bore and a longer stroke cast crank. The cast iron crankshaft didn't spin balanced, so a small offset weight on the flywheel (or torque converter) and a small off set balancer weight allowed the cast crank to spin balanced and was less expensive then adding special metal to the cast iron crankshaft. It didn't have anything to do with being better, it was about the cost of producing millions of motors using the cast iron crankshafts instead of the forged crankshafts. Chrysler started playing with other cast iron crankshafts as well, with the 400 big block (the emission replacement for the 383), the 340 in its last couple of years of production, and the 440 in its last years of production. All of the cast cranks used the flywheel/converter and balancer weights specific to the motor, except the 318 cast crank, which had the shortest stroke.

Fast forward into the "new" Magnum motor series. It was originally built as a 5.2 (318) with a short stroke cast iron crank that didn't need extra weight to balance. Then, because of demand, the Magnum grew a 5.9 (360) which still needed extra weights to balance to spin properly, but not as much wight as the LA 360's longer stroke needed (I believe the 5.2 and the 5.9 Magnum motors have the same stroke).

Who knows how close the tolerance between the piston weights or the rod weights are these days are, but its still pretty clear that a 5.2 (318) crankshaft must still spin pretty close to 0 balance and a 5.9 (360) still needs extra weight to spin balanced, but the LA 360 balance is not the same requirement as the 5.9 needs.

Your options are pretty clear.
1) Buy the flywheel and balancer for either your LA 360 or your magnum 5.9 and use all the pistons from the same motor and all the rods from the same motor and hope for the best (I suspect it will be fine up past 5,000 rpm).
2) Find a machine shop that can balance the entire rotating assembly, including the crankshaft, the pistons, pins, rods, flywheel, and front balancer, and pay the price.
3) Hope someone has a Cristal ball and can magically tell you exactly what you have.