you'd be better off buying a header for it. it will be extremely loud, so buy a muffler for it if noise is going to be an issue where you ride. if you don't want to spend the money for a header, weld up a straight pipe using water pipe for it. it's galvanized so you don't want to breath the fumes off it during welding.
basically, you don't want to go hacking up the stock muffler. remember, you got to pay to play.
btw, if you buy a header you might have to heat it up and bend it some to make it fit. my AGK header wouldn't fit because the frame was in the way. i ended up having to bend it out a bit over an inch (at the end, heated it just after the bend) to get it to clear. it's running outside the frame which i'm not too excited about but it works. i've only hit my leg on it once and i wasn't even riding it at the time (barely got burned). header wrap will help to keep from getting burned a bit too.