Just a suggestion, but you could use your resin dome and some cloth with polishing compound on it. Leave out the center pin and oscillate the drill as you turn it. That should help alleviate the circular grooves in the head. What the others here said makes a lot of sense, as taking too much metal out of the head can change the size of the combustion chamber, but if you use a fine cut polishing compound that should slow down the amount of metal taken off when compared to emery cloth or sandpaper. Just a thought.