Yes, I believe a 700R4 will fit, but I think you will have to modify (shorten) your drive shaft. You might also check into a 2004R auto. I think this is a smoother swap than a 700. If memory serves me, it will should swap in about like a th350. Check out
www.firstgenfirebird.org and do a search on the subject. There has been quite a bit of discussion on this swap there.
Good Luck, Bruce