There is no way to tell simply by looking at it, and no way to say if it is even stock, likely, but then half the swaps owners are not aware of. The ratio is not cast on, it is stamped into the axle tube. The chrome cover is not original. Do the old spin the wheel and count the driveshaft turns, but that's based on also knowing diff is not worn and if it is posi or standard. To be sure, just pull the cover, check the old oil for any rubbish, count the teeth or check the stamped numbers on the sides, add new gasket and fresh oil and know for sure.