Just my opinion but here it goes.
Those are the original production u-joints, see the plastic "nubs" sticking out from the sides of the end caps through the yokes. Non greasable joints, when he disassembles the shaft for shipping that will render the u-joints unusable as the O.E. joints were designed to not be reused once pressed out of the yokes.
The nylon was injected into those holes at the time of manufacture. IIRC the replacement u-joint was GM P/N 7806140. The shop manuals warned against attempted reuse of the original u joints as there was no way to retain the caps.
The Double Cardan (centering ball) used at the middle and rear of the prop shaft was another problem. Trying to remember back 40+ years, if correct there were two designs of prop shafts,and again if correct the early 71-2 shafts were not able to be rebuilt using the GM Parts Division service part but the 73 and later shafts were. But again, I think most good driveshaft repair shops could work their way out of this issue.
For what this information is worth....
