Like Fred said, the Eaton H0xx series axle started with the 47.2 trucks and kept going through 72. There were several gear ratios and widths available, parts should be relatively easy to find at your local Napa or Car Quest. The internals of the carrier changed slightly around 63 or 64. Search for Eaton axle on here, everything you can want to know has been covered (except whether the later finned brake drums are the same size as the earlier smooth drums...I'd like to know that myself).
