Yes, that is also a very good point. The factory rocker arm geometry is designed for valve lift of roughly 0.400 inches. Which is exactly what you would expect since that is what the lift was when those heads were designed in the late 50's.

To keep the geometry correct, you have to lower the rocker shaft into the head 50% of the additional lift. So if you go from 0.400 lift to 0.600 lift, the rocker shaft should be lowered 0.100.

The only reason to use shims if if you are running less lift than the original design of 0.400. Most people don't do that.

The problem is that if you lower the rocker shaft it moves away from the valve so then you need a longer rocker arm. Best fix for stock heads is to mill off the pads and use offset blocks like the factory designed for the W2. Then you can lower the shaft and move it into position. But then you need to modify the pushrod holes and all of that jazz.

I think the serious class racers used to do all of this stuff years ago. Not sure if anyone still does it anymore. They probably just send their heads to Jesel for modification if Jesel valve gear is allowed in the class rules.

I wrote up all of this information years ago in a magazine article and then covered it again in my big block book. Not sure why I'm bothering to type it in again here.