Thicker gasket makes up for head material removed. I am advised it is better to be too thick than too thin.
Regarding the prechamber measurement, 7.85 is mid point of 7.6 - 8.1 range. Mercedes recommends seal ring (shim) .1 greater than needed and not more than .3 greater than needed. If prechamber starts at 8.1 and .127mm (.005") is removed, measurement is now 8.227. A .6 shim would be my choice.