The mufflers in the above picts are Super mufflers, they have a grille on the front of them, your muffler is likely from a non Super. It is easy to get a Super muffler off the Bay, they usually go for $20-$25 and are easier to modd than the regular 028 muffler.
Pioneerguy600
Maybe Jerry knows something I don't, but if you have the really early muffler with the extra little side mounting screw and the "speed nuts" built into the back half of the muffler case, then you can't just mount on a super muffler, because there are no threaded holes in the crankcase to mount the front of the muffler to.