Just a little more info:

Took her out for a drive last night, got her warmed up good, brought her back and checked the damper oil again. The dampers still move nice and slow at temperature, so I think I can rule them out.

Also finally got around to pulling the plugs again (they look fine, no difference from one to the next) and did a compression check. Front to back: 120/120/120/125. Not exactly great but not surprising (the engine does have 98,000 miles on it), but more importantly no discrepancies between the cylinders to speak of.

Called Delta yesterday and ordered a Pertronix distributor and Pertronix coil. Crossing my fingers that that will solve the issue. I’ll be really ticked if it doesn’t, because I am running out of ideas…