That's an interesting idea. The last good Firebird was built in 1973. 1974 was ok and 75 started the decline.
One correction from the post above though; The wrap around rear window started in 75. If I were you, I'd look for a beaten up 70-73 Firebird, then clone it out to a Trans Am or Formula. I have seen some really nice looking TA clones. You wouldn't be able to tell without looking at the title & serial numbers.