are you sure you have a T5, Borg-Warner sold out to Tremec in the middle 90's, I think they kept making them for a couple more years, I don't know if the Tremac took a different driven gear, you may have a different Tremec transmission altogather
I have done some research on the T5, Tremec still makes the T5 for the V6 Mustangs, the drive gear and the driven gear are still the same as the old Borg-Warner, the newer ones have electronic sending units instead of drive cables, I have found an interesting article on the T5 check it out:
http://www.ffcobra.com/FAQ/speedo.html