You, obviously, can get about as many different answers as you want. I have been using a pinion depth-setting gauge, and a dial indicator. But, I have listened to, and watched, one of the set-up guys at Tri-County Gear (Pomona, ca), and this person used nothing but his 'pattern-compound'. His feeling is, that using the gauges, only get you 'close'. He never uses the gauges for the final pattern. On-the-other-hand, I've had pretty good luck, using the gauges. I often get a good pattern on the first try.
No matter what you do, my advise is to not try this without 'set-up' bearings. Tri-County uses them, Hick's uses them (and, me-too). In my view, you will just frustrate yourself, if you try to do the job without them. (Some of the gear parts sources even loan these bearings. But, no problem to make your own.)
To address your question about setting pinion depth, using common machinists tools... I have done this, and it works fine. The point is, the pinion depth is from the center-line of the ring gear/ carrier, to the machined-face of the pinion. Use some ingenuity to figure this out. You need any machinists depth measuring devise. The cover surface is machined, and you need to assume it is 'square' with the pinion. Put the carrier caps on, no bearings, and measure to the nearest bearing surface, farthest bearing surface, and the pinion surface. Do the math, and you will have the pinion depth. Target depth numbers come with the gears, and the variance is etched on the pinion (like, .001, .002, etc.) So, for a 30, the pinion depth target could be 2.252 (2.250 nominal, .002 etched on pinion). Or, for a 44, the nominal is 2.625, add the variance, and you could have a target of 2.627, or whatever.
A picture of this, and instructions, comes with new, major-brand, gears.
Bottom line... This is in the instructions, too..... The final pattern is what counts. And, all the measuring can either help you, or not help you.
An experienced person, with set-up bearings and compound, can do this in about a half-hour-to-45 minutes. Most 'newbies', would spend a whole day, and still not have any confidence that it is 'right'.
Good luck.
bobH