Are you still running the T-5? I'm doing the V6 to 393 swap on mine and had just planned on running a Tremec with a mechanical input to a Autometer speedometer.
This info probably doesn't help you but may give you something to think about. Have you tried posting on all the other major boards.........Corral, Stangnet, TurboMustangs.......You might even want to try STLMustangs.com and PM the owner Bobcat. He's a T-5 guru.........
Mike