Welcome! You've got a 400 in it now. Might be easier (and cheaper) to have that one rebuilt..Pontiac 400's are hard to get your hands on plus, when done right...their beasts....but the great thing about Pontiac F-Bodies is that they came with Pontiac, Chevrolet, Oldsmobile, and even some Buick motors during the late 70's.
That being said, just about anything will fit in your Bird. I've got an 87' 350 block in mine. All I had to do was get Chevy engine mounts and swap over the battery tray to the pasenger side.
If you do go with a Chevy Block, you'll need a new Trans since Pontiac and Chevy motors have a different bolt pattern to the bell housing.
This post has been edited by 81frbd: 07 May 2009 - 06:32 AM