I just remembered my mechanic saying something about bending points leaf to make more pressure, that's likely the source of my issue.
Too much pressure on rubbing block, extra friction, boom squealing, dry rubbing block.
Which likely wore prematurely, thus closing the points gap and screwing with timing.
You'd think it would take a lot of extra pressure, but maybe not.
Bending the points isn't going to change the pressure on the cam at the rubbing block. The only thing that will do that is changing the spring on the points or moving the pivot point away from the cam. Basic geometry says that.