Just wanted to point out, that the centered spring solution here, is way better engineering, than just removing one of the original springs.
Definitely that's right.
I might buy a selection of springs to try the impact of different ones. Sad to say, I lack both the equipment and the engineering skill to modify the piston, though I might try a thicker head gasket to make more space above the piston. As far as I can see, the only other variable that would affect is the exhaust push rod and there is a bit of latitude there to adjust that easily. The limiting factor is probably that just adding a ten or twenty thou head gasket would not make much difference to a 7cc engine.