It's those "nasty belt oscillations" that I'm worried about. This is
definitely a 3-groove pulley, and it's definitely out of whack, at least
horizontally. I certainly have never removed the pulley on this VWoC
remanufactured engine, but maybe the PO did for some reason. It doesn't look
like the kind of thing you'd do for fun.

I'll try tightening the belt down some more but I've always been afraid of
killing the bearings that way. Both Bentley and Haynes are near useless on
this point: the belt is supposed to deflect 10-15mm when pressing "firmly"
with thumb, but what does "firmly" mean? Arnold says one thing, Maria
another. Vast difference.

Yeah, this is a primitive design, with the alt/wp belt contacting maybe 20%
of the drive pulley. It seems like to make it work you have to tighten the
belts way more than you would with greater contact surface, leading
to...premature bearing failure. I bet some ingenious guy could come up with
an idler system that would help us out. Any takers?