rchase is exactly right. You can see on posts 23 & 24 above how I was measuring the backlash. You need that dial indicator tool. That's not necessary on the lunchbox locker for the reasons rchase mentions, and it's not necessary for either one of them to mess with the pinion depth.
The whole point of the carrier is to put the ring gear true-to-center and true-to-perpendicular around the rotational axis of the axle. That axis will not change, no matter what carrier you use, so the ring gear's depth in relation to the pinion also will not change. Therefore you don't need to deal with the depth of the pinion. You only need to concern yourself with the side-to-side position of the ring gear, which is what controls the backlash.
And it absolutely will change. I thought that I could get pretty close by just measuring minutely where the ring gear mounting surface was on the old carrier, versus on the new carrier, and adding shims to make them equal when they were on the bench with the setup bearings in place. But as everyone correctly predicted, that turns out only to get you in the ballpark -- once it's under tension during a test fitting in the axle, the measurements were still many hundredths off. I believe I was about .030 off, which is way out of spec. Thus the time-consuming process of taking the carrier back out, adding and removing shims, re testing, etc. Then installing the real bearings only after it was 100% right.
I was impressed at the fact that the setup bearings were so close to the real bearings. The difference between the backlash during the test phase with the setup bearings, versus the final with the real bearings pressed on, was only .001, which is acceptable. And my Jeep has not exploded since, which is the real test.
Edit: should have made clear, when I said backlash will change, I was talking only about when you install a new carrier like the TrueTrac. Not for the lunchbox locker.
My do-it-yourself install thread for a TrueTrac in the rear, upgraded shafts, and a PowerTrax No-Slip in the front:
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