I have a good understanding of backlash (setting ring right and left)

and good idea on pinion depth (reading pattern depth and gear mesh depth) seen images of how it should look

I realize this is a pro's job but to me it seems tearing down an engine and rebuilding it is way more complicated, I don't hear that being pushed off on pros?

I always figured back in the day hot rodders didn't just go to a mechanic every time they wanted a mod they just dirtied up their hands and went after it!

Pulling apart an engine would have 100's of parts laying around my garage, but looking inside the differential seems I can count the parts on both hands.

Several years back I tore a 1966 jeep cj5 apart down to the frame(parts everywhere), welded on it (never done before) threw new suspension on it, ran all new wires, built a dash, put all back together and bounced it off rocks and dunes for 2 year before selling it. I believe this is the true spirit of any restoration or project. If every time you need to do something you ran to a mechanic no one would learn anything and no one could afford to rebuild anything.

BAck to engine rebuild, setting pistons wrong. gaskets wrong, timing chain wrong, valves wrong etc would cause catastrophic failure. Setting gears wrong would? make them noisey? make them wear sooner than normal? The worse case in my mind would be running with the gears so poorly set that they were binding and they blew up. But I don't think I would put the cover back on if this was the case?

Bought back lash gauge for couple bucks, got bearing seating set, seal puller, got a garage with a lift and all the wheels off the ground, only specialty tool missing in my mind is a bearing separator and press? I see hillbillies in you tube videos laying in the dirt on a cardboard box changing gear sets, just because they have changed them before are they pros?

If I am oversimplifying it some one please chime in