A few years ago when I had my heads off with the old cam I was getting just a wee bit of detonation on the tops of a few of the Pistons. I brought a spark plug into the machine shop and it was way too hot and I'm pretty sure the AR 3934 s are what he sold me or that was the heat range and I changed brand but I don't think so. But I did now LOL... 220 lb of cranking compression, I may be dealing with a combustion chamber heat issue?
When your cranking compression is that high, you will need to pull a few degrees of total timing out of it, unless you are running high octane fuel. I'd put thicker head gaskets on it next time you have it apart. My opinion, of course
