Take your old pinion bearing and grind out the center some so that you can easily slip the bearing on and off to get the pinion depth set correctly. avoids haveing to press the bearings so many times!
I made my own Pinion depth guage out of some 1/2" tool stock(any straight edge will do) and a sliding caliper. Lay the tool stock across the the 2 flat surfaces that the caps bolt to, then rest the calipers on the edge of the tool stock and measure into the pinion(using the plunge feature of the calipers), and then subtract the 1/2"(or however thick your straight edge is) for the tool stock. All pinions have the depth marked on the gear end.
This is only a starting point, tooth contact pattern is the only true test of your pinion depth being right.
The short answer to your situation is to start out with what was in it and go from there, no two rear ends of the same type will likely be the same set up, so it is trial and error.
Make sure that you have enough preload on the pinion when checking tooth contact.
Make sure you have the carrier bearing preload/gear backlash set properly before checking tooth contact.