Why not swap in an LS-1 with a 4L60 trans? With 3.73 gears and the overdrive the 4L60 has combined with the lockup converter you can get over 20 miles per gallon and still run a 13 flat 1/4 mile using all stock parts! I have seen several of these on Camaros and Firebirds of your vintage and they really aren't that expensive to do if you shop prudently in wrecking yards for a good donor car. Don't forget the LS-1 is all aluminum so you're not planting a bunch of excess weight on the front end.