rear end woes

What a great idea. You can also use a pushrod and calibrate the thickness of it as zero in order to get a accurate reading from the top of the push rod to the pinion face.
I have to give a shout out to Paul Cangialosi at GearBoxVideos on the pinion depth measurement technique. I have heard it described by some heavy truck mechanics I know but he shows doing it with a Dana44 Jaguar center section. So much simpler and quicker than most of the fixture tools used to set pinion depth.