Great info Don.
I did experiment with building my own belt. I was never happy with it. I'm sure it's partially skill based. Also looked at gravity molding my own, but the required mold size is just too big to be practical. Instead I'm using these:
https://us.misumi-ec.com
1mm thick, width in 5mm increment and custom length in 10mm steps. Only cost $10 each for 50mm x700mm
Tracking was exactly my concern the fixture above was assembled with great care to try and get everything as square and true as possible. Just to see how much adjustment I really need. Tracked OK, but not perfect. Crowned rollers might be exactly what I need. Should be able to modify what I have to see how it acts.