Well, "assuming" you still have the original rear end and driver's door, the best way to check your gear ratio is to check the door tag. Next bet is to see if your rear end has a tag on it. Usually, if the 3rd member has been removed, the tag isn't reinstalled.
Do you have a tach? Yet another way is to see your RPM at a given speed.
More than likely, you have a 2.80 gear ratio
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