OK I give up!
I found a 741 case (correct date code / PN for what I'm trying to do) with Power-lock and the gearing I wanted that looks to be in usable shape or at least rebuildable for a great price. If the gears are trashed I want to be able to get a replacement set in the same gear. But the gear selection for 741 seems limited to 3.55 and 3.73. Rockauto says they have in stock, "US Standard Gear" in the ratio I want, for a 741 case, but I don't want to gamble that they will be available by the time I can get the rear in the car and tryout the OE gears for noise etc.
Guess I'll keep looking
Thanks All