Serpentine belt tensioner is jumping and acting weird

Problem found!
The AC delete pulley has three mounting holes, through which 5/16" bolts go through and into the front cover, as shown in jos51700's post #3 above. The holes are significantly bigger than 5/16" and there is thus a lot of "adjustment" possible.

What was happening is the pulley was too far back and the belt was trying to jump over the front of it, or getting hung up on the edge. I've pulled it as far forward as possible and cranked down on the bolts and it is running smoothly.

Not too excited about the prospect of constantly having to check the AC delete pulley and will be looking for possible solutions for taking up space in the holes. But it works! And it works well enough that I was able to run the car around the block for its maiden voyage. Tomorrow is an alignment in the morning and then spend a few hours beating up the car on the highway to see if I can break anything... then off to the races!