Some of the STX cams were mushroom tappet. A pain, but they worked.

Jim, I think that the rule is just now being enforced, and the angle milling the head is what they do. I was told by a well known AH builder that they have "evolved", though, where the valve angle is not quite as critical.

Michael, the charge passing through the chamber on the overlap cycle has always been a problem at high rpm, simply due to the location of the valves opposing each other. They have seemed to alleviated that somewhat. The new rocker gear and related geometry has certainly helped, but it was not the complete answer.

All this work was at Barnett's shop in Georgia, back when we are all young and virile, Michael, and I don't recall your being there. We ran the Barnett's ex Pro Stock Arrow in IHRA T/S in the mid eighties. Even messed with nitrous in the early days, but that's another story.....