Wes, in my old (1941) Machinery's, there's quite a lot of info on leather drive belts: US Navy Dept specifications, including tanning for 6 to 8 months with white or chestnut oak, where on a No 1 native packer steer hide the belt should come from, pre-stretching, lap-jointing including direction of the lap and glueing, laced joints, thickness and width, belt speed etc etc. Maybe you could get hold of a similarly vintage Machinery's.
That said, unless you want to set up your own tannery, it would probably be easiest to buy the belts but if you think anything I have might help, send me a PM.
Andy