1980's came stock with a 3.45. The coupes had the 3.90s, but I've seen many a car with the rear end swapped out. The 3.08s only came in the 2800 or so TR8s, and the 81 TR7 automatics. Good luck trying to find one. Another longshot would be to find a rear end out of a Rover SD1. You could swap the ring and pinion into your pumpkin. The only problem with that is the parts to rebuild the rear end are even harder to find than a spare 3.08. That is why so many TR8s are running the 3.45, and why so many people are building Ford 8.8 posi disc brake rear ends to stick under the TR8s. The 3.45 will yield about 70 MPH at 3000 RPM in fifth gear.