As well as the different TO bearing, the 72 has a bigger pinion bearing. I prefer this bearing instead of the early one, since its bigger in diameter, and longer than the early one. Being bigger it should be able to take more abuse before pounding out the bore in the case. That being said, the early ones do work fine in high perf applications. Geoff has the tiny one in his car.
A 72 will have fine tooth gears, the 64 will have coarse tooth gears.
72 with 4.12R&P:
3.8
2.06
1.26
.89
64 with 4.37R&P
3.8
2.06
1.32
.89
Both have the weak 10 tooth mainshaft that must be changed to a 9 tooth if an engine is 2275 with slicks.
The 64 may have a steel 1-2 shift fork, the 72 will have a weak brass one.
The 72 gets a backup light switch.
There are also lots of other minor details that are different.
Tire clearance and brake size are the only two functional differences between long and short axle transmissions. The long axles in the 72 take the larger 68-up rear brakes.
