Im running an 18 foot 78 charger bubble deck jet, stock Berkley with 502 with AFR heads. I recently had it in the machine shop because my motor ate the windage tray, machinist was as blown away as I was with the situation and how it happened?? But I got the motor back from machine shop and ended up having to take it back due to some machining issues with the heads, upon inspection, on top of the machining error, my machinist said I was about to blow a head gasket (we had put maybe 5 miles on the motor at this point.) Machinist said possibly due to detonation. So pulled timing out, changed to a different spark plug (running the recommended plug for the AFR head I have). I run 91 pump gas unsure of my compression ratio cam lift is 635 intake 640 exhaust 112 lobe separation. But I was out for memorial and blew the head gasket, my water temp is running about 150 degrees, I have water flow coming out of the pisser on the side of the boat and I walk my boat into the shoreline to ensure there is not any sand going into the engine. I have 20 miles on this motor now and the passenger AFR aluminum head is toast now. Any input would be greatly appreciated.