Hey everybody,
I'm a newbie to firebirds. I just purchased an 87 bird. I was thinking of swapping in a 350 for the 305. But i had a question, what is the difference between the pre-87 350's and the 87 and later 350's. I was just curious what the difference is.

 

One piece rear main seal instead of 2 pc.

The 4 center bolts that hold the intake manifold to the heads is at a different angle.

Center bolt valve covers.

Roller cams started entering the scene.

 

but you can use the newer block, newer then 87, with older perimiter bolt heads.

 

If your talking about pre 87 350's in 3rd Gen cars the answer is there were no 350's in those years. For GM's other lines and models it was mainly two piece main seals & four bolt mains in trucks.