I've built mine and two others now, all with different kits. One truck with the gmax kit got sold a year later so idk how its doing now...
I learned allisons in school, and this ended up being the fastest and easiest way but too expensive :rofl:
I have a genuine Allison manual that I use, and there's a ton of info there that isn't in the atsg books. I went cheap on my build, but I never plan on building a motor, and it'll blow before the trans does. Having a lathe/mill near by is handy as you will very likely need to shave the backplates to get clearances.
IMHO, the average "good" mechanic can tackle an Allison rebuild and install a kit and set clearances. This is not a "build" like Mike or Evan would set up, that takes a lot of trial/error and a deep understanding of how the systems work together and what you're trying to accomplish.