I put a straight edge over the block tonight and nos 1 and 4 do not potrude. I tried pulling the offending piston up with a valve grinding sucker, but could not get adhesion.

I thought some pics might help.

Piston No1, you can see the shiny part where it looks to have struck. There is no obvious damage to the piston or the head fces. Just no carbon build up.




The opposite piston for comparison. You can see a carbon covering as expected.



The undersige of the head, - No carbon on the opposing side:


Closeup of just that combustion chamber. Again, no obvious striking damage, just the lack of carbon.