So far as I know the 52 and 72 punkins are the same internally, although the '51, 5.13 had an adjustable block that rubbed on the ring gear to limit lateral travel under heavy load. The later '67, 52 with 4.57 didn't have that.
I have a punkin with what I believe is a good pinion bearing but the gearset has just too many miles on it and is noisy and has acid-etched pits on the gear faces. Someday maybe I'll run across a good 5.13 gear set and can reuse the 5.13. There are circumstances where it would be helpful.
