I went to GM and looked through some old dusty books. No luck.
I called Richmond Gear and they said there is an alignment dowel pin that is pressed into the bearing retainer plate. That pin locates the tail housing and the case. And NO they don't sell the pin. So I hope maybe I have the pin in with all the zillions of old needle bearings. But even if I find it...how did it fall out in the first place?