The flywheels will interchange. If the flywheel has a weight on it its definately a 454. 454 was the only external balance BBC made. The balancer will be weighted also.

wrong again,the 502 is externally balanced.a gen 5 and gen 6 454 and 502 with forged crank use the same balancer.

What length Rod is in the 502?
Never mind you right.

Cant remember if i have ever seen a gen 5 and 6 flywheel attached to a gen 4 crank but it seems like a few peoplehave modded the mk4 blocks for later gen 5 1 piece seal cranks and rear cap . Ill bet mike knows off the bat if forged and cast call for different flywheel p/n. Me , ill have to go look in the gmpp book

im pretty sure the forged vs cast crank engines use different flywheel.

I put a mark iv crank in a gen 6 block. I want to say I used the gen 6 flywheel but it's been awhile.

Thats what i was thinking , absoluteley different balance on flexplate by couple ounces but cant say for sure on flywheels . Been bugging me .going to have to go pull the p/ns now

Just found out it has 14096188 heads also has L128 cast into head and GM 2 CFD cast into head.,
UPDATED IMAGES here:
http://phoenix.craigslist.org/nph/bpo/5107629626.html

Thanks for all the input.

Gen 5 454 mag!

That explains the valve covers .and the fuel pump .