Was a different driveshaft used than on the stock "K" code and was the driveshaft used for an automatic different than with a manual transmission?
I'm curious too, is the auto driveshaft a different length? If converting from an auto to a T5 or Tremec, is a different driveshaft required?
Believe the length is different and would need to double check on the dia and end yokes Have no idea on the modified application but would guess that yes the driveline would need some modifications
The '66 GT350H I looked at today had been converted to a 5 spd and was able to use the same automatic driveshaft with the setup he installed. (It also had an hydraulic operated clutch if that is a clue)