Back axle pinion shaft conundrum

[Stuart Giles]

I also noted that the bearing carrier is probably scrap (should have looked more carefully before).  The rearmost bearing has been turning in the housing and worn a noticeable grove. 

If you're talking about the relieved area in the "top hat" where the two Angle Contact bearings live, later ones came from the factory like that, the AC bearings are there to take the axial load, the ball race immediately behind the pinion takes the radial load.  Have you got the "old" pinion  ball race available to compare the widths.

Edit: should learn to type faster.