Will that pipe you cut out is what I used as the stinger on a couple of the silencers I built. I keep mine about 1-1/2 to 2 inches long so it doesn’t hurt performance.
Always protect your hands when using power tools. I was drilling a hole in the muffler cap. I was holding the cap down on the floor of my porch while drilling and the bit got stuck and the cap spun out of control. I ended up with a deeply sliced pinky finger tip. Probably would have gotten a couple stitches if I had gone to the er. I just had my son bandage it up and it's fine so far