Stopping the knock: Lower compression and ported heads...

okay, I just finished reading the whole thing, if you were detonating, you'd see some evidence in the pistons, at least, I'd think.

You mentioned running one stage colder plug, I'm wondering if you need to go one more step. My runs a 68 cuda with a 472 stroker, talked to him about your issue, he said he has something similar happening and dropped plugs he said were at least 2 steps colder and the problem went away

probably a cheaper shot than pulling heads over and over...