I had rebuilt GM, Ford, Catapillar, and JCB transmissions 25 years ago. A Good manual, Snap ring pliers, Clutch Drum Spring compressor, and a lathe helps, (for reworking seal grooves) are required. I used to get Good kits and manuals and used hard parts from a place in Texas, I believe it was called Bulk Auto Parts. I will check my books and the internet to see if they are still around. Good manuals could be had from “Automatic Transmission Service Group”.
https://atsg.com/about-us/
They now charge a fee for membership though.