You didn't mention if your TransAm diff was a disc brake unit. I've used several 3rd generation Camaro/Firebird diffs (62")with factory discs on my 54-3100 and they work great. The replacement parts are a bit pricey but the performance, along with front conversion discs and a MANUAL mid-70's Corvette disc/disc master, adjustable proportioning valve and both residual valves is outstanding. If your diff is drum, than IMHO, conversion to front discs would be highly recommended if you plan on driving it in traffic.
I've got some pics of both the disc and drum conversions in my "shoebox" album. I hope this helps.
