Try searching the site for the info on the Harley Dyna conversion.  Pics, model and part numbers were supplied.  One HD muffler bolts right up with no alteration, although you must use a Harley clamp.  This subject was discussed at great length.

It needs to be what is called a 1 3/4 inch pipe.    That size can be made to fit, but .... the Dyna's are easiest because of 1) muffler has a welded on bracket that lines up fairly nicely, 2) On the Dyna's , the cross-over pipe to balance the system in on the header pipe, where on a few sportster models it was it on the muffler.

It should be noted that the OEM take-off sort of shoot the exhaust by the rear brake linkage and can cause soot to deposit.  Can look meesy.... unless you are going for the Rat look.

I used a dyna muffler. I had it installed with just a 1 3/4"x 1 3/4" adapter from the 'Zone. Had a hard time keeping it sealed even with the Harley muffler clamps. Have put a bind on the connections to line everything up. Finally had it welded up with about 4" piece of 1 3/4" pipe at a muffler shop. With just a kink (by the tech section 6-7 degree bend) in the pipe you won't stress the header end and you will miss the rear brake with exhaust. Best thing with the dyna besides the cross-over (or lack of it) is it has the same type of rear mounting. I could only get one on due to the length but it has been appx 3000 miles with no problem.  Best $30 dollars I have spent on Suzi.