Drain the oil, pull the cover off the back. Take a clean rag and wipe down the small round face of the pinion. There should be a number stamped on the end of it, the part number and ring and pinion tooth numbers.
I still havent seen any marks on the housing, but most of the stuff Ive dealt with is at least 50 years old.
Theres also some numbers inside of the teeth of the ring gear, one will have the part number and one will say 6-37 (6.17 ratio) or 7-38 (5.43 ratio), respectively they mean number of pinion teeth by number of ring gear teeth.
As Ive already pulled apart several with the 6.17 ratio, the part numbers are; Pinion 3652549, Ring gear 3652522. Im in the process of rebuilding mine right now and am derusting and cleaning all the parts involved. I imagine the 2 speed rear ends are pretty similar, but I havent taken one apart yet to verify.
Hope this helps, Jeff
