I appreciate the replies.
All fittings came in sealed packs, with what looked like genuine BRP packaging. I would not be shocked if these were mislabeled, and were intended for a Yammy or some other motor. Cheap knock offs maybe; who knows.
Even so, I shoulda figured this out earlier.
As long as I’m coming clean, I’ll also admit I assumed my spark wires were OK since they bench tested as fine, and looked great. Eventually I moved them to mimic twisting of the distributor while testing, and they showed how very broken they were. Maybe this explains why my troubles varied, with different throttle positions.
Onward!
Many thanks, and happy motoring to all.
Alan