Seeking some advise

SG4247

Could be a couple of things....

I would look at,

Extra compression from reduced deck height, .020" larger bore diameter, milled heads and larger piston domes will cause detonation with low octane fuel. Prolly need 96-98 octane to be safe for regular driving. I would pump some 100 octane into it when it is nearly out, and then drive it, see what happens. Depends on your tune, as to how much timing the motor will tolerate without detonation. If the sensors see knock signal for very long, that will put the engine in limp mode!

Also,
Piston hitting the head, decking the block, coating the pistons etc... it happens. If the head gasket thickness wasnt increased to offset the other changed dimensions, then interference can happen. Seen it.