Here is the rest of the story.
I offered a significant re-design to the owner, including adding crown (minor) and building a new motor cradle to put the center of nutation at the center of the driving drum (major). Cost was more than he wanted to pay (since he already had been given a new Jet equivalent as a replacement for the Powermatic.
So per the original deal he offered me, the problematic Powermatic became mine.
And suddenly a craft project of my daughter appeared, that needed a belt-sander (making chess-boards out of log slices)
So now I had to make the thing usable
First, I added crown, about .020 on both driving and driven drums (several very high-tech helical wraps of electrical tape)
Then I completely removed the gearbox that drives the cam that rocks the drum from the back end of the motor. That included the fan cowl, but over a couple of hours use the motor only got sligthly warm.
The cam action was opposed by a spring. I replaced the spring with a little pipe spacer bushing, so I could adjust with shims and lock the drum angle solid.
The belt (after a little adjustment) now tracks well enough. Shifts a little as you bear down on the work, because the long motor shaft that carries the driving drum deflects. Needs an outboard bearing. Only two other drawbacks remain. One is that the cam used to loosen and re-tension the belt for installation has too little travel,and the spring it drives is too short. There is essentially no allowance for slightly differing belt lengths. Also the motor is feeble..not too hard to stall it, sanding a 12" diam oak disc.
But it is now a usable machine..