If you don't know the basic setup distance (from the back side of the pinion head to the center of the carrier bearings), there isn't any tool that is going to help you. It won't help you to measure the pinion depth, if you don't know what it's supposed to be. The only way to do this is trial-and error with gear marking compound.
Make yourself a set-up bearing, install the pinion and ring gear, and read the pattern. Disassemble, adjust the pinon depth shims, and try it again. Keep adjusting until the pinion depth is close. Then adjust the backlash with the carrier bearings. Once you that where you like it, you will most likely need to readjust the pinion depth. Back and forth, in and out, over and over.
Remember, adjust pinon depth first, then backlash second. It takes a while...
The road goes on forever, the party never ends....