Backlash I can handle -- I did that when I set up my Torsen. Since I was swapping diffs, not gear sets, I didn't touch the pinion.

Has anyone ever used this?

http://www.ratechmfg.com/pinion%20setting%20tool.htm

It's a gauge that sits ON the pinion shaft and provides a measuring surface between the bottom of the bearing pocket and the gauge itself. There are models specific to the rear end being set up (#10006 is the one for the Ford 8.8.) At $30 at Summit, it's cheap enough for me to grab and do the rear end myself. If I install the pinion and can't get a good contact pattern, I can always have a shop re-do it.