Again what Dennis was saying about Pinion depth, a new set of gears should have a depth measurement on the pinion face. This will be the distance from the face of the pinion to the carrier center line.

I worked with an old machinist to set my gears up a long time ago. He made his own tool for doing this. It consisted of aluminum donuts that bolted in the bearing carrier caps. Then he had a bar that ran through it. The job consisted of pressing the bearing on and off several time to get the shims right. He would measure between the pinion face and the centered bar. Then we had to subtract 1/2 the measurement of the shaft to find the center. I don't know if any of that description made sense but most tools for doing the job are similar.

A used crush sleeve and honing out a extra set of pinion bearings would make the job way less exhausting. There should be plenty of youtube videos on the subject.

I have an engineer guy at work that setup his own gears in his daily driver. He used a fish scale on a breaker bar to set the preload for that 15inch/lbs. The factory service manual is also a great resource.

I myself have a great place in town called Saddler Machine that does my gear setups. I can take them the whole rear all ready to go and it maybe cost a few hundred for the peace of mind. Not trying to discourage you just a warning. I have seen some shade tree mechanic types way screw up a whole rear end gear pattern. I'm talking gears whining really bad going down the road. Once its messed up you can maybe reduce the whine but not completely get rid of it without a new set of gears.