Hy dgallagher, yes a differential from a 60s-70s automatic could be an improvement, be careful there were differentials of different manufacturers in those years. As for identifying without removal, on the end of the pinion there may be some numbers stamped, some will be the part number, some might be the ratio expressed as 35-7, divide the larger number by the smaller number and you get the ratio in this example 5.0 to 1, hope that helps.
