Guess there is more than one way to skin a cat. Not everyone has a good machinist straight edge or blocks though, I don’t.
I have the complete tool from T&D. It sits where the carrier bearings ride. Was expensive back when I bought it ($300) but I’ve had it for over 20 years. It’s way more now unfortunately. Those $120 universal anodized pinion depth checkers are garbage.
But beyond the pinion depth tool you’re going to need all the other tools as well, just no way around it.
Here is an article on the Ratech tool which is super cheap.
https://www.hotrod.com/articles/t-and-d-machine-pinion-depth-tool/