So when you put a 440 crank in a 400 block, the minor issue is the counterweight diameter.

383 cranks have a counterweight diameter of 7.125.

On 440 cranks it is 7.500 diameter.

The difference in radius is only 3/16".

It looks to me like 383 counterweights have more than 3/16" clearance around the bottom of the bores.

I've been told you have to machine down the 440 counterweights when you build a 451, but now that I'm
looking at it, it seems like you don't need to.

So I'm wondering what other 451 builders have done. If you keep more metal on the counterweights
it would be easier to internally balance.

Clearance to the piston skirts, maybe?
It's been a long time since I built my 451 but I think the machine shop turned the counterweights to 7.25".
Using KB280 pistons and Eagle H-beams a small amount of heavy metal was required.

Mock it up and spin it. Clearance it where it hits.

Just got one ready and dynoed. Using 440 LY rods, and cutting about 1/4" from the outer edges of the counterweights next to the main saddles with a fly cutter. Turned out just fine. I used KB "quench dome" pistons for that application, cut the domes down with a lathe, and the crank balanced internally. Nothing special in it, Comp XE275HL hydraulic flat tappet, RPM intake, RPM heads and a 750 Edelbrock AFB. Factory electronic distributor, Hooker A-bode fenderwells + 3" exhaust with mufflers. Made close to 500 hp

Once you build one you'll know.

I think you will need to chamfer the crankshaft counterweight at the bottom of #6 cylinder around a 1/4 inch on the # 4 main bearing side to clear the bottom of the block.
I've had more than one 440 crankshaft machine to fit into 400 blocks along with offset grinding them to 2.200 BB Chevy rod journal size to get 3.91 stroke and had the mains cut down to stock 361/383/400 main journal sizes, I'm pretty sure the machine shop ground that edge down to clear the low deck blocks as part of the package to fit them into the low deck blocks
7.25 sounds right as far as the counterweight O.D., maybe not

Andy's old article states 7.25"
http://arengineering.com/tech/451-manifesto/

Because the bottom of cylinders are lower on B than RB blocks. The extra clearence helps on keep safe the rotation assembly, specially after engine get hot, where metal expands

It ain't gonna work, because the bottom of the bores is closer to the crank CL on a B engine.

Feel free to grind the crank, attempt to drop it in and see if it will rotate, to see what is happening.
That is what I did, and right after that I cut the CW to 7.25 OD.

A tiny bit more material needed to be removed for balancing
with typical 1.32 CH forged shelf pistons.

Both of your assumptions are wrong.

OK, thanks everyone.

It seems there is a small possibility I am mistaken ! Never happened before.

Will proceed with caution, trial fitting, etc.

Would knife-edging the counterweights accomplish the same thing?

Maybe but it isn't very economical. The basic issue is that a 440 forged crank is way too heavy to balance a 451 with performance rods and pistons. Also, the edges of a 440 crankshaft will rub on the main web area. Cutting the counterweights down to 7.250 is a fairly easy process and it solves both problems.

The length of the bore in a 383 is 6.25", I would guess the same in a 400.

So from the crank centerline to the bottom of the cylinder is just under 3.75". This would be a diameter of just under 7 1/2".

So I guess the 7.5" diameter counterweights on a 440 crank would indeed be too close.

Does anyone know the bore length in a 440 ?

The first one I did some 20+ years ago with a forged crank, I clearanced the block. Using ROSS pistons and Eagle 6.76" rods, the counterweights looked like Swiss chees after balancing, so it truly makes sence to cut down the counterweights in a lathe. This time around I used a cast crank with LY rods and KB pistons, and didn't want much external weight. So, only chamfered the outer edges of the counterweights next to main saddles, and it worked just fine. And zero balanced internally.

Interesting somebody made the stroke with a Cast Crank. LOT of ppl told me not to do it due a probably hard balancing process job, so I sold the 440 cast crank I found and couple of years later just by casuality, got a forged piece

The first one (and the last) was started in the early 90's with inexpensive parts I hade purchased on the cheap. 66" 383 block, polished the factory 383 rods, TRW 2315F-030 pistons that I cut down .175" off the top on an old Wynona head milling machine. The underside of the pistons were trimmed with a carbide bit and die grinder. The crank mains were turned down to 383 size and the counter weights were cut to clear the block....THEN I had it balanced. Aaaaand $1000 in and mallory metal later it all fit together. It's currently apart getting freshened. I think there's 6 or 7 sticks of heavy metal in the crank counter weights. Live and learn.

Since the original build a second set of TRW slugs have been made with valve notches, shortened pins, and piston pin locking rings to accomodate Eagle 383 rods added. I still haven't learned.

It would have been cheaper to buy stroker pistons but that is a common mistake. I've seen lots of people try to build cheap motors who end up with stuff that doesn't work.

Anybody with a bare 440 block, what is the length of the bore ?

Are you asking from the bottom of the cylinder wall casting to the decks? I have a 12.0 inch dial caliper that I can get close with if that is what you want
I have two stock 440 bare blocks in the shop, a 1970 SPD cast in June of 1969 and a 1971 .