His tranny is an SM420.It does have the original torque-tube .
I am guessing that his u-joint assembly has broken.I had the same problem with my 52 GMC 1/2 ton where the yoke which slips on the driveshaft end cracked and peeled the tube part of the yoke off the yoke itself
It was a little difficult getting the twisted metal off the end of the driveshaft but once it was off, the replacement worked fine on the shaft end.
