Rear axle bearing puzzle

[flatheadfan]

Another quagmire... I pulled apart a '36 differential only to have the roller bearings and cage fall off one of the differential sides. Nothing seems broken or bent. Why it fell off is a mystery. It appears that the bearing was replaced sometime in the past probably a old stock aftermarket part. The other side- no problem. Looks like I will need a new bearing and race but, what? Evidently, Ford in '36 made two different axle bearings, There must be a difference. Does anyone have a clue how to tell an "early" from a "late?'

If it is any help, I've enclosed two pictures of what I am looking at.

Tom