I really don't know, and no one will be able to give a straight answer because it could be anything: 2.56, 2.78, 2.93, 3.08, 3.23, 3.36, 3.55, 3.90, 4.11*, 4.33.
I am fairly certain that 4.11 and 4.33 were a dealer intall option.
What you can do is check the top of the axle on the passenger side, or maybe a tag bolted to your diffi. Although that doesn't work most of the time, on my 69GTO it is rubbed off. But there is another way. Jack up the back of the car, and use jack stands for safety. I found my ratio by spinning the rear wheels in neutral, but I have heard that it can be in gear and by spinning the driveshaft. Put a chalk mark on your driveshaft and the U joint lining up. And another mark on your rear tire straight up.
First find out if you have a posi rear or straight axle by rotating one tire, if both tires turn in the same direction: posi, different straight. For straight axle rotate the rear wheel until you get one full turn of the driveshaft. Guage how many turns the tire has done. Multiply by two. Thats your gear.
For posi, don't multiply by two.