I was there as the valve train as a possibility when the old engine was in, but now this is a brand new entire 2F build that is exhibiting the exact same issue as the old 120k mile tiredish 2F.Valve seating is important to vac. Something could be going wrong when it heats up. Crud on sealing surface should be blown free by the compression. Any heat expanded burr might be knocked off/down by the impact.
Spray testing everything while acting up might produce different results than when everything is cold.
Different Head, different engine, all new components but same old intake manifold and header, nothing else was carried over.
The Sniper, Dist, is also brand new and we have the exact same initial issue.