The problem is this: An iron/steel rod typically needs .050" growth room in an engine, and the aluminum rods need more. Checking this in a cold setting will give you a clearance that is not there in a running hot engine. That piston seems to be touching the head where it is shiny. I have seen 427 pistons with the combustion chamber imprinted on the top of the piston when hot, but check OK cold, with .038" being minimum head to piston clearance with steel rods. That aluminum block may be moving more than you imagine when under load and stress of combustion heat. This may be a detonation slap causing the piston to rock just enough to hit the combustion chamber on that side. I would check piston movement at TDC with the clay in that area and then measure it again. Joe-JDC
