I know most of them, butt still missing some information related to rotating assembly. Cranks are different for sure, heavy duty vs. light duty.
But how about pistons, rods, balancer and flex wheel? Are they of the same weight early vs. late?

 

There's not a whole lot of info that goes to that level of detail. What is your goal? Are you trying to build an engine with the parts you can find locally?
Flex plate and balancer will interchange as long as it's a 350. They may look different, but the weight offsets will be the same.

I know the 403 rods are different than the early 350 rods. Did they use those same rods in the later 350? I don't know.
Cranks did change over the years, generally getting lighter. You can still swap cranks just fine with the earlier ones generally considered stronger than the later ones.
For rods and pistons I would keep a full set together if at all possible. I think I had three sets of various "small block" rods at one point and all three had different weights and shapes.
Pistons are likely to be a similar story. But if you're buying old used parts hopefully it's cheap so you can get a few sets and weigh them.

 

The RWD flexplates will interchange. Engines bolted to TH325 or TH325-4L FWD transmissions used flexplates that are smaller in diameter than those from either RWD applications or TH425 FWD applications.

 

Pistons changed a lot over the years.
The very early 68-70 engines had 12cc (9.0:1 compression), 6cc (10.25:1 compression), and flat top (W-31 only, 10.5:1 compression) pistons.
1971-1972 engines had HUGE 23cc dish pistons (8.5:1 compression ratio).
1973-1976 engines had 14cc dish pistons (8.5:1 compression ratio).

I have no idea about the later 350 engines.

 

The windowed block, shitty 3A flowing crack prone heads and lightweight crank are the big differences. A member broke a crank in 3 places behind a 400HP 403 with 6 spd manual that was abused, in their defense. They are even a lighter colour grey than earlier cranks, are lighter with slightly thinner counterweights. The mid 70's flex plates look the same as the later ones marked Metric. There are basically two balancers on the later motors, the tiny hub and full size balancer. I know they started putting the small hub in place of the full balancer on the late 70's Olds V8's. The pistons and rods should be identical to the mid 70's and earlier 2bbl 350 14cc pistons and rods. It depends on what you want to do with the later 350, whether it is a good starting point.

 

[QUOTE=oddball;1457056]There's not a whole lot of info that goes to that level of detail. What is your goal? Are you trying to build an engine with the parts you can find locally?
Flex plate and balancer will interchange as long as it's a 350. They may look different, but the weight offsets will be the same.

Few years back I built a stroker 374 with -69 solid web gas block and N-crank, E-brock heads and roller cam. My goal now is to build kind of a b-engine from leftover parts. It will not be a performance build by any means, just a spare engine to keep my 69 cutlass alive if I ever would like to work with my a-engine.
This will be minimal budget build. And I really mean Minimal. I have a 69 350 block with it's original pistons and rods. But i don't have a matching heavy crank. I do have late 350 light crank and couple of 307 cranks. They look pretty much the same.
What I'm after, is it possible to build a decent 350 short block with -69 block, rods & pistons with light duty crank, without running into balancing issues? Balancing work is now out of the question because of minimal budget. I hoped someone would have the information if the light vs. heavy cranks weight offset would be same or not.

 

The balance would probably be different, but for a backup engine I bet it'll be close enough. It'll just shake like a Chevy instead of purr like an Olds.

 

Do you have the later 350 pistons and rods? There will be a balance issue just because of the counter weight differences, let alone the material difference. Can you get away with swapping cranks in a temporary motor? Maybe. I cooked the crank in my first 403 due to repeated overheating. I had a good 307 crank, I installed without balancing and new bearings into the 403 with the full size balancer. I ran it for 5 years, including multiple 1/8 mile runs. I eventually spun rod bearings after revving to 5500 rpm. For temporary, low usage engine, throw in rings, new bearings and have a spare. It probably had a full size balancer, use one. Sounds like it would get minimal use, go for it.

 

I have a pile of parts and I think there is an uncomplete set of late 350 rod/piston set. Still good for weight comparsion.
If you have run 403 with 307 crank for 5 years, I should not have too much of a problem. In fact, I've heard a local guy here had a same combo, even raced with it. Lasted together for several thousand miles. I think I just button the engine up during the winter This engine will never see high mileages.

 

:d:d:d