Hunting ingnition timing at idle

That sounds like the piston hit the valve and the valve deformed the bucket in that story. But if that happened I believe the damage to the valve would be extensive and the head would have to come off immediately. Why that one was so far out of spec for me is (?) is dont know. But I know this. Pulling the head, disassemble and inspect would tell the story. But believe me once I got them, and the one, adjusted. I have a sweet idling engine again with decent consistent leak down pressures between the cylinders for its age and no more cold start misfires.
But from now on, if its this truck or another 1st gen that I have the valve clearances will not go ignored.

 

Great way to guilt me into finally checking mine. Need a warm Saturday now