Out of the 7 ht builds I've done, I had one that ran great but knocked badly at high rpm. Sounded like the piston was hitting the head.
I removed the head, saw no interferance. I put it back with 2 head gaskets anyway, and it was better but still knocked when wound up.
Pulled the jug off and discovered about .012" up and down clearance in rod play in this new engine.
Bad machine work at the factory. Runs quiet below 5000rpm though.
I sold it to someone who drives very conservitive. He sez he has heard no knocking.