would i be better off putting a 400 in my 87 Iroc or a 383 stroker?

 

Depends mostly on the 400 block you have available, and what you plan to do with the car when complete.

Easy driving, 400.

4-bolt 400 block with some healthy power, you might be better off with a 383.

Factory block, 500+ HP, 383. Or Motown block.

Motown block, why stop at 400?

 

If you have a perfectly good 400 crank and block, build a 400. Don't go wasting a hard to find 400 block by salvaging the crank to make a 383. If you want to just turn a 350 into a 383, buy a new stroker crank.

Nothing wrong with a factory 400. They haven't been produced since 1979 and there are still many driving around. They were never produced as a performance engine. Poor cam and heads held it back from making any power. A few aftermarket parts can really wake it up.