You would be far better off to adapt a Turbo 350 or a 700R4 to your engine, and find an open-driveline rear end.
I agree.
But if you insist on figuring out how to adapt an automatic to the torque tube there are a couple of other options.
The 4-speed Hydra-Matic was offered in torque tube trucks in '53 and '54. It would be a factory parts conversion but you end up with an old design transmission that is expensive to rebuild and does not drive as smoothly as
modern automatics like the TH350.
Or you could engineer a torque tube adapter for a modern automatic similar to what Patrick's has done for the Saginaw 4-speed. Do a good enough job and you might find you could make a small fortune selling such a thing provided you started with a large one.
