I seem to recall finding some sort of incompatibility between the way the center support bearing and splines on my PV driveshafts vs. a 122 OD shaft I had. I think I looked at them a while, then just ordered a new PV center support bearing and took it off to get shortened ($75).

Refreshing my memory via the WWW.GCP.SE online microfiches:
PV center support bearing:


122 old style center support bearing:


The PV front section ends in another flange, which bolts onto the front section of shaft to secure the center support bearing. And the yolk has the holes, the car has the little pins. On the 122 it is somewhat simplified, with the splines built into the end of the front shaft. It might be possible to use an entire 122 shaft, if the flange at the diff is the same, but you'd have a relatively minor issue of the car *and* the center support bearing having pins, but you could drill one or the other out to accept the rubber bushings. But then there is a marked difference in the height each bracket holds the driveshaft at in relationship to the pins/busings. The center support bearings don't interchange, either.
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'63 PV544 rat rod, '93 Classic 245 + turbo