Valve pocket/bowl hog tools....

HF electric die grinder with carbide burrs (mcmaster carr) and router speed control. Dont know that I have much more that $150 into it all.
Make a fixture to hold the head firmly in position. Slant six rocker shaft works and allows it to rotate.

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It's interesting how stable the 6" long carbides are. I thought they would chatter all over the place. I think you don't force them too much because of their length.