I recently replace the ring and pinion in my '52. Upon disassembly, the ball retainer on the double row bearing was gone. So, obviously the pinion bearings got replaced. Upon careful inspection, the carrier bearings were in great shape. No perceptible wear, scoring, etc. I reused them as replacing them later is not a big deal as you don't have to mess with the depth of the pinion gear when removing the carrier. From my research, the pinion bearings are the most common failure point in the rear differential.
