Thanks for the input
I talked to Reg at BDR and the T-56 will fit (and he has one in his car).
I realize the TKO600 will take more abuse. However my intension is to use the car as a street machine with the occasional trip to a road track but not real heavy abuse. And I think I'm just inside of the limit of the T-56 ...provided I don't put slicks on.
The 2 overdirve gears is more atractive to me (this way I don't have to decide which final drivegear to go with and I can shift as needed

).
The rear ratios available are 3.15 -3.25. I am leaning toward the 3.25 as I don't need a crazy top speed.