I'm pretty sure this has been covered before but I couldn't find it
All else being equal with rest of engine build, 80s d250 2wd, 3.55s, NV4500, carbureted small block, same short block with either head choice, same CR, same cam, in a truck that will be towing at least half of the time it's rolling, would cast iron or aluminum heads be better? Probably 80% relatively flat Midwest area ..

If the heads were identical I doubt you would really notice in a truck just driving around. Moderate weight savings using aluminum, but trucks are already heavy in the first place so that is a wash.

Most manufactures aluminum heads are different from oem cast iron heads so they should work better if they are newer than old Chrysler stuff just based on being closed chamber for starters. However, you can still screw it up by getting aluminum heads that are inappropriate for a low rpm truck engine with ports and/or valves that are too big for the application. On a truck you'd want heads sized for mid-range grunt in the rpm range it will be used in.

Nice things about aluminum heads: lighter, more octane-tolerant, probably better velocity & more-efficient chambers.
Main thing, as Neil says, is low-mid range for that application - essentially standard port/valve velocity over area.
Also, if the need arises, aluminum is more easily repairable than cast iron.
Also depends on budget and what the existing iron heads need.

Ok then if I either had both available or the original heads were "shot" and had to replace anyway... Which would you go with
If the choice is aluminum I'm not looking too hard at speed master actually because of the Chinese thing.
If aluminum I was thinking Edelbrock.
If cast I have a good original un cracked set of factory magnums. (One of which is NOS/ never been on an engine) Would actually like to find another. (Swap meet season is coming back)

Years ago Hot Rod did just that test. Using otherwise identical, or as identical as possible, heads with the only difference being the material used there was zero measurable difference. Now this was on a well built street type engine, no stupid compression ratios, no power adders, no real lopey cams, etc. Compression ratio was around 10:1.

This was on an engine dyno, so in car, real life might be different. But any one that claims one head has an advantage, other than weight or cost, over the other has no data, that I am aware of, to support that.

I would go with the aluminum heads, they have improved the design over the older cast iron heads. Also, is your engine able to use magnum heads? You said it was an 80s but not which. Finding another NOS head might be difficult? The cheap route would be factory 302 heads, they were an improvement over the older factory heads. Don't forget the SM black friday sale, when they have about a 40% off sale, you can get a nice set of cnc ported heads a lot cheaper. Though there is no guarantee they will have the sale but if I am correct, they have had the sale every year for at least 5 years in a row now.

I dunno, the 302 heads, stock, have small ports and a closed combustion chamber. I ran them on a mild 360 for awhile, 340 cam, 4bbl. Nice torque increase, lucky to hit 100 on the top though. With J heads I could do 130+. But realistically, neither top speed is needed on the street. All this in an 87 Diplomat, A833 and 2.94SG.

5.9 heads would be ok if he can find another one that doesn't need to be rebuilt. Putting 5.9 heads on an old LA block requires you to do extra stuff so be prepared for that.

I don't know what it's like where the OP lives, but here machine shops want as much, or more, to redo old cast iron heads with new guides, seats, valves, and a valve job so many people just buy new or already remanufactured heads thru the parts store instead. My dad was quoted $1600 to go thru a set of GM iron heads a few months ago. Also, the shops here that are good are backed up so you might be waiting months to get them back. The shop that gave him the quote didn't even have time to do them either as they have months of backed up work scattered all over the floor. Lots of people here are just buying a new crate engine with a warranty rather than having old stuff rebuilt as the down time does not work for people who need to get their vehicles back on the road.

I have a set of 302 heads freshly rebuilt standard machine shop overhaul.... New stock valves.
I was gonna put those on my 78 fury when I de lean burn that one....
That engine has its original '163 open chamber heads still on it that it was born with...
That car's a story for another thread. Not what the engine build this thread is about.
I have another set that needs to be seen by a machine shop, '714 casting, (same exact heads as '302s) under the bench.
I could redo that set for this build, like I said this isn't a race engine I'm scoping out, but a torquer for a 3/4 ton tow rig.
I don't ever expect to wind it out much past 4k or at least not very often, certainly it won't ever see 5k.
But wanting to use what I got for this truck engine, i have 2 ea 318 and 360 magnum short blocks here and I am going to base my build on one of those. Not sure if I'm gonna build one into a stroker yet or not. That truck actually surprised me with it's original 318 when I put a stock 360-2 bbl cam into it and an EQ magnum top end into it as to how well it did set up that way. when it had its original untouched 727. I have some choices here to pick from.....
Like I'd originally said I do have a set of uncracked stock magnum heads here, as well. IF I don't buy aluminum ones somewhere those will most likely be what gets used.
Thinking of building a 360 with flat top pistons close to zero deck, with a healthy RV torque type cam.
I have a couple of ideas there as well ... That also will be a question for another thread once I get my short block decided on.

Yeah the machine shop I have been using the last few times hasn't done me wrong yet but they definitely have a long lead time to get anything done.

the only downside of just buying new assembled heads, aluminum or iron, is can the machining and assembly of said heads be trusted without a complete disassemble and check of all components and machine work ?
if something is off, how much is it off by, and now what do you do ?

Yeah I know. The last set of new "bolt on and go" heads I bought (EQs) bit me in the azz big time. Was the 3rd set of EQs I've bought, 1st of those that were both drilled as factory magnum heads (manifold side) and "ready to run". They weren't. I didn't find out until I bolted them into my Durango and it stuck and bent a couple of valves with less than a couple of hours run time, cost me a fresh short block as well as a result.
Which is why I'm very leery of buying any brand new ones.

that has been my fear, and without a disassemble and check of the complete valve job and guides, plus a spring check including the installed height[s], i wouldn't feel comfortable at all.
this does not include a chamber cc of all chambers, which if off, or indicates a [large] variance from end to end, will need the head milled to correct that discrepancy.
man, it never ends, does it ?

I can't seem to install anything without having to rub on it a bit - and stuff like guide clearance, valve job, and springs/retainers have always needed addressing.
Doesn't matter whose heads (Eddy/440Source), though the Indys I had on the 512 were already installed and seemed fine.
I haven't had TFs or Speedmasters; my Batten W2s were quite nice, but my guru still checked 'em over, don't recall any significant tweaking.

If I gotta take them apart or send them off and have that done then why even buy new?

my career machinist talents [?] have me checking, measuring, checking, measuring, tweeking, checking, tweeking again, measuring, adnausium, on anything i do anymore, so i then wonder why i never get anything done in a "timely" [?] fashion !