use a thin paper material. Yamaha uses a thin paper material for cylinder head base gasket and the same thickness stainless metal sheet for head and cylinder gasket it has raises ridge around combustion chamber about 1/4 from inside wall. it flattens when torqued. I would use thinist paper gasket material you can find and use ballpeen hammer to cut out using cylinder wall housing (make two) use a sheet of the thick aluminum fol=il glued between the two gaskets and glue. use right away ( use pencil to open stud hole in foil) after one side of gasket is glued to it and holes are made you cn apply sealer to other side of foil and position 2nd gasket. This with insure you stay close to your original compressin and have strengthener in it. Also easy to remove if you screw up! don't forget to apply on both metal faces too (cylinder and head )
david
david