the numbers on the differental that indicates what variation it is.

Casting numbers are on the top of the diff. If its in the car, you'll need a mirror.

If you want to know the ratio, you'll have to open it up, as its stamped on the crown wheel.

the numbers on the differential that indicates what variation it is.

For one thing the R-200 is larger than the R-180 . The two studs on the rear of the diff are larger on the R-200 . The numbers are stamped on the ring gear but you would need to remove the rear cover . What are they out of ? If you know what Z the diffs. are from, then we can tell you what they are, and the gear ratio. Automatics have 3.54 to one and manuals 3.36 to 1 MOSTLY . Some 2 + 2s have the R-200 with 3.70s . Zs with 5 speed tyranny's have 3.90s . so you see it helps to know what the Z was that they were pulled from . Gary

The stamps on the ring gear will be two numbers offset by a colon, such as 39:11 (3.545) or 37:11 (3.36).