IMO, I don't think its going to be as cheap to do up an LS1 as you think. I've priced it and know a few people. If your planning on making any major power power, you gotta deal w/ the rear end, tranny, + suspension first thing before touching the motor. You may want to do more research.
Also, I don't think now is a good time to get an old F-body. There way over priced around here, I predict there prices to drop a bit when the new F-bodies come out...