I forget which but either pre-ignition or detonation. One of them can cause a hole in the piston. Many things can cause this condition. Some which have already been mentioned. Gas, timing, lean, etc.
I dont plan on having that much compression, maybe around 195 to 200psi at the very most. I got a cr ignition and as far as I know its set at the stock position. I did test out the spark and it makes a pretty big blue spark, even with a old plug. do you think maybe a b9es plug would work a little better? I dont understand completely how the "hot and cold" heat ranges work, I just know that the hight the number the colder the plug.You said something about getting the cylinder decked because the gasket leaked, that could cause the piston to be burned like that.
Sucking coolant & then times sucking in raw air & causing a way lean condition on top of the piston. I could see it happening, but I would still check the ignition to be sure its set right & go to the race gas for sure. Race gas removes a lot of guessing, at least up to a certian compression amount. Compression up around 230,,,250 lbs, you near bout need to check race fuel if it came from a service station.