Very carefully. The hole spacing is very close. I took a drill about the size of the hole for the muffler in the engine. I moved it back and forth and enlaged the holes. You have a lot of meat to play with on the ends, but in the middle there is much metal. This is where you have to be careful. You could also drill out the muffler and run the screws all the way through and put a nut on it. Dubro makes a 50mm by 3mm screw which should be long enough.