I do have an old set to place in when working in the chamber area. I have fould that the 120 grit dremil flapper bits work the best when doing this area. They are perfect. I did some more today and they are coming along nicely. I now see why people wan't so much money to do this. It's not because it's hard it's because it's hard on you. All the metal and carbon in nose and lungs, ears ringing and more. But if you have the will you will win in the end. On that note don't be scared to port and polish.