There are a few tricks you can do with the heads to lower your compression ratio, and since your engine isn't together these can be done easier. First, use tulip valves in both the intake and exhaust. Second, un-shroud the combustion chambers around both valves out to where the head gasket fire ring is. Third, polish the combustion chambers. You can even, un-shroud where the valves open into the cylinder, again use a used head gasket as a template (to locate where the fire ring is after it's compressed) and go no farther into the cylinder than where the top ring rides. (pic). When assembling the engine use the thickest head gasket you can find.