Piston Class is in !!
I'm more confused than ever
OP said 340RPM heads.
With the .060 relief cut
To make room for the nominal, +.045pop-up, 340 domes.
leaving .015 clearance..... plus gasket thickness
is about .054 with an .039 FellPro, or .045 with the .028 gasket.
mathematically speaking.
Where's the problem?