I just used the diamond pistons calculator
6cc piston dish. .240” top ring down.
4.18 gasket bore.
Piston .010 down and yr 67.5cc chamber.
11.1 with a .040” gasket
10.8 with a .050 gasket
@Miszny If your or cookietruck’s calculations are correct, build it and send it, your in where you need to be. As stated earlier, I’m running a 11.09-1 - 360 engine on US pump 93 octane without issue. Intake duration of the Hyd roller is 224@050.
Go for it!