The example was at 2000 rpm, or they would have kissed the pistons.

I actually made an Autocad drawing of the exact shape of the quench area of my heads (302s) and had the pistons made to that drawing.

I have found the same thing as the testing did. Way less detonation and way less timing (about 60%) than open chamber.

I think .035 is too tight, even for a steel rod engine. I run .038 , and I think that is on the edge, but I only go to 5500rpm. Once you get to about .040 everything has to be perfect, and you need to preassemble and check every cylinder for piston height in the bore. Even with very careful machining, and redone rods, I had almost .004 variance hole to hole. I did rod repositioning and got rid of most of it, but still had to offset bush a couple of pin bushings to get to under .001 variation.