I think you could use a Vette or Jag rear end that mounts the center section solid, and use a CV type joint between the tranny and rear-end.
I also think you could modify the tail housing, and output shaft to make the slip yoke slide into the rear of the main case, by machining a new plate to house the rear case bearing and the rear seal of the tranny. Leave the radiator up front, pipe the water back to the engine, scoot the bed back about 2 inches from the cab to allow air flow around the engine, (May require some scoops)
Fab a belly pan for the old engine compartment with ducts to let the air coming through the radiator out at the wheel wells. Mount a crossbed toolbox with the bottom cut out in the front of the bed and put a tonneau cover over the rest of the bed and you have a verrrry serious sleeper!!!