MK-
Welcome to the Stovebolt. Good question.
If the truck is indeed an original '50 3/4 ton, the driveshaft is enclosed between the transmission to the rear end U joint within a steel tube/pipe known as a torque tube. Later models (after '55 I believe, but certainly by '57) had a single steel drive shaft. Others may correct the details here, but the '50 vintage truck had a unique driveshaft set up. It will be straightforward to upgrade to a steel shaft if you are swapping out the rear end.
Does this help?
