My '06 backfired stock and still does.  I have a '07 dyna muffler on mine. I rejetted and what a difference in performance. Not familiar with the sportster muffler myself. There is (or at least was) a tech thread with the different Harley muffler installs. You will need about a 6 inch piece of 1 3/4 " tailpipe with a 6 degree bend in it. The Harley exhaust clamps are nice because they are heavy duty. Some foks have used auto muffler clamps. The Dyna muffler has the slotted mounting setup just like the factory muffler. I used a 1 3/4 inch adapter piece from the zone. A winter project is to redo with the proper pipe with the bend. I have over 5000 miles on mine this year as is but I have the head pipe and muffler in somewhat of a bind. I would rather get it proper and then have it all welded up. I keep getting small leaks from being in a bind which contributes to the back fire. Plan on rejetting. Your bike is as lean as it can be from the factory. When you open up the exhaust you will be way lean!! Check the different signature lines and the where the bikes are. My jets with about 1/3 of the original carb spacer is good for the 299 ft altitude in Memhis TN. If you are in the mountains you need to run leaner jets. Check the spacer mod thread and Lancers carb tuning thread along with the muffler. An easy afternoon project for all if you are familiar with wrenching a bike. A full day taking your time. Enjoy and welcome!!!!