Let us know what you decide to go with, but FWIW, I would reccomend first the Tremec and second just go to Sterling Ford ( local Motorsport dealer) and buy a new Z tranny. 703.430.3673 Talk to Joe Hill and mention Colin sent you his way. Maybe he can help you out in some way. They have helped me out quite a bit with many parts for my race car.
Best of luck.