Steve- Check out the January 19, 2014 posting in "Transmissions and drivelines" headed "Looking for torque tube 50 sedanette." You will find specifics for a (relatively) straight forward move to an open driveshaft and strong rearend.
(I also have a 1951 48D, converted from Dynaflow to standard 3-speed, which I learned was anything but a simple task. Good luck.)