Remove head and check for a true flat surface. I mill the head as little as possible (couple of thousands) with 200-320 grit DA self stick sandpaper. I stick a sheet onto my garage window and rotate head and cylinder surface until I know it's true. Surfaces will look like new aluminum. And replace gasket with a thin gasket from SBP. If too much is shaven off, the clearance can be too close and might close the spark plug gap. Additional gasket/gaskets might be needed.