How do I ID a 4 speed, overdrive or not?

Well I ended up getting a great deal on a narrowed 8 3/4 out of a 70 Duster. It is is about 4 inches shorter drum to drum than a stock A-bodies, and it has strange axles with the 5 on 4 1/2" bolt patern. And it looks like the spring perches will line up perfectly with my Duster with the 3" inboard spring kit. But for now it has a 4.88 sure grip chunk!!!!!! I'm probably gonna put it in the car as is for now and have some fun before buying or trading for a 3.91-4.10, gotta save up some $. Should be interesting!

Butch