I have never seen that. But I don't mess around. If I need to mill for compression, that is what I do. In reality, high performance requires a cam and better valve springs. But if I had to choose between a cam and better heads, I would pick heads. The engine does not care how it gets the air, just that it gets it. If the heads can flow enough air at a certain lift, it does not matter. We spent a lot of time searching and finding the best head castings, Mopar, Ford, and Chevy before we started on the rest of the engine.