ok,
now it's sure that the 1-1/4 turn on the "H" jet was borderline for the Xcan but,..................
not getting to see the plug from that time period you can't say for sure what of the stuff you found on tear down was done by the jetting at that time.
i had a light scratch on the cylinder and piston when i first got my engine new, you might have too.
the stuff near the ring and the skirts, was it graduating toward a blueing and hard surfaced, or was it tanish going toward dark and able to be wiped or lifted off with a finger nail ?
the diff. being the first is heat, the second would be something you'd expect to see if the exhaust was blocked and the engine was trying to run against the resistance AND on the resultant RICH mixture.
on the other hand, my Dom vibrated loose at the port once, that causes a lean run and very high idle, you know to shut it off instantly.
just some thoughts,
steve