[BigAls87Z28]

LS7/L92 heads will fit on anything with a 4 inch bore in the Gen III/IV family, so the LQ4/9 and LS2 blocks will work. Car Craft did an awesome build using STOCK L92 heads that flow something evil, with a decent cam, making 500hp easy on pump gas, and for under 5 grand. This was also carb'ed...

377 would be a coo idea too, would rev higher and have a the 400's larger bore, similar to what John was talking about.

Of course, if you are gunna stick to the strict rules of Trans Am, in a 69...its gotta be 302. A Gen III 302 would be fun to build too, but realy...I would just spend the money on a high po Gen III/IV.
The LS2 comes carbed as a crate engine.