You can find out what's out back without too much trouble. All you need is the ability to jack up the rear end of your car, and knowing how to count helps too.
If you have a car with a posi or limited-slip rear, jack up the car and get both rear tires off the ground. Get the car up high enough so that you can get your hands on the driveshaft to turn it. Make a mark across the pinion yoke and onto the rear end with chalk or a grease pencil. Do the same to the tire on the car, so you can see when the tire has rotated exactly one turn.
Now count the number of turns of the driveshaft that it takes (use your chalk marks) to make the rear tire rotate ONE time exactly. If it takes about 3 and a quarter turns of the shaft, you have 3.23 or 3.25 gears. A bit more than 3, you have 3.08s. Very close to 3 and three-quarter turns, 3.70 or 3.73 gears. This method won't work very well on a posi that's worn-out, one that won't spin both tires equally.
If your car has a one-legger open rear, jack up only one rear tire and leave the other on the ground. Turn the driveshaft and again count the number of turns, but this time you must make the tire do TWO full rotations. This is due to the 2:1 ratio of the differential spider gears.
Sorry I can't help you ID it by using those numbers, but you can at least find out what ratio you have without doing a teardown.
