I did the math and keeping the stock deck height of 0.025, and a fairly standard gasket of 0.040, I'm getting 9.37:1 compression (feel free to double check my math, probably screwed it up). I'm finding places say PSI is usually 15 to 20 times compression, so I think I'd be in the ballpark already without changing anything.
A stainless steel shim gasket at 0.015" thick would get me up to 9.9:1, might still be under the 180 PSI limit with that