yes there should be a tag on the rear dif cover under one of the bolts denoting the gear ratio.
But if not there
Jack the car up and put it in neutral. Make sure you can spin the passenger tire on the rear.
Ok now turn the passenger side wheel slowly.
You must count how many time the tire spins to 1 complete turn of the yoke.
so for example:
1 complete turn of yoke and the tires spin close to 3 1/4 times then you have a 3.21
Also while you have the car jacked up spin the passenger side tire and if the drivers side turn the same direction at same time you have a sure grip if it spins opposite you have an open rear end