I drove a 93 cobra with a T-56 viper spec just today, felt really notchy!!!!!! Almost like a gate shifting lambo or ferrari... However it still felt very very (very) stable at the speeds I was going.. (65 - 120) and no vibration..
I think the vib. comes from the driveshaft not the tranny, but that is my opinion.
i don't understand why the t-56 is dismissed so easily here. in my eyes it is the most practical tranny out there. yes the final overdrive is not an upgrade, but fifth can actually be used in racing. think of it like buying a tko road race tranny with another overdrive. as for the torque rating, i think they have that low number to ease thier warranty absorbtion rates.
What kinda trouble have you had with g-force or the others. Is this more a support issue? I like the idea of just changing my clutch disk and rear yoke on my drive shaft.
The more I think about it I would be better off with out the dog ring setup, and just run the spiral cut gears with syncros.
From what I understand the vibration comes from the whole setup. If the bellhousing isn't indexed (with an aftermarket bell), or the hieght on the cross member isn't correct you'll get vibration. I think thats what I experienced. Just look at how many "TKO swap trouble" threads are on here. Thats why I went with the G-Force and haven't looked back.