If you are tearing it down, just replace all the bearings since you are in there. Especially if you don't know the history of the rear end. Unless bearings are somehow expensive for the old rearends, there is more cost in the labor, and if you are planning to dissassemble, just replace during assembly, there is no extra effort, just some marginal cost. Then you know what you have and you have new parts for your normal wear items.
I don't know about the older ones, but on more popular rear ends they will sell a rebuild kit that basically has everything you need in it. Pinion bearings, crush sleeves, carrier and wheel bearings, bearing races, gaskets, even the marking compound to check the gear wear faces.
