Rear End Question

[Martin64]

Is there a way to tell what the gearing of a rear end is just by looking at the outside of it?

Here's the situation, one of my neighbors moved out and left a rear end in the car port. Management had it moved over to the dumpster, which just happens to be next to my garage, and low and behold it has 6 lugs and drum brakes. After closer inspection it has a "GM" casting on it in raised letters. So right away I figure it's a 6 lug GM rear end that, with just a little luck, may be the 3:08 that I'm looking for.

I've moved the rear end into my garage so I can figure it out.

There's also another way to tell but I forgot how. Something about turning the axle and counting the turns at the yoke and multiplying by some number.