Identifing Diff's
 

I have an 80 RX7 which i'm upgrading everything to SE spec. The 80 RX7 already has Disk brakes with 4x110 lug stud style rotors. When I turn the rotors or drive shaft everything turns, which I assume means this diff has LSD

I also have an 84 GSL-SE diff with large disk brakes and 4x4.25 studded rotors. I plan on swapping the SE diff into the 80 RX7 because I'm upgrading the front suspention and brakes to SE spec I want the same bolt pattern on the rear.

Both diff housings look identical and I have an idea that the diff in the 80 RX7 is a SE diff with GSL axel's

Is there any specific features that would identify what diff is in the 80 RX7? Specificly what size bearings are used without pulling the axels?
Also would there be a way to tell what gears are in the diff by turning the driveshaft and counting the rotor revolutions?

Thanx in advance

Divide the number of ring gear teeth by the number of pinion teeth.

any other suggestions?