I've got a 700r4 that I was wondering if I could stick into an 81 Corvette. The 'vette has a 3-speed (don't know what kind of tranny specifically), and 3.08 gears, so gas mileage is definately suffering. Would it be possible to swap the 700r4 into it? (both autos, of course.)

This is a common swap. You should do some hunting around on www.corvetteforum.com for more info on this. If that '81 is rather stock the 700r4 should hold up fine. If you have upped the power of the engine I would stick with the th350 that it has now. They are much stronger than a 700r4. Good Luck.