On my original mufflers, I knocked out the baffle plugs. It sounded better and ran the same. I used a 1" steel round jackhammer bit with a point on it.
I took the mufflers off, cleaned them really good then wrapped them up in cloth to keep them from getting scratches. I put the muffler on a piece of old carpet to soften the end and went at it with the bit and a hammer. Then decided it was better to just drop the muffler down on the bit on the floor. Got it stuck and had to have my buddy help me get it out