For those of you running 78-79mm pistons what are you doing to keep compression ratio reasonable?

My spare race prepped head has 27cc combustion chambers and combined with a 79mm flat top piston and .8 gasket the compression ratio would be 14-1.

Are people using custom head gaskets (79mm gaskets are .8 & .6) , dished pistons or do you just run 110 octane fuel.

I have easy access to 100 octane and would like to keep the compression at 12-1 or slightly below. The A15 I just blew up was at 11.89 but unfortunately the head on that would need significant work to be fixed (10mm wide passage between combustion chambers) that head had 29cc chamber.