Original thread on Dyna's is here, but the photobuket crap has the thread hard to follow. Some part# references are buried in there:
http://suzukisavage.com/cgi-bin/YaBB.pl?num=1298689417The direct bolt-on part# is supposedly 65747-94. Others will work too, but some you don't want if they have the crossover pipe. The ones with the little 'buttons' with female threads are mountable, but you have to make a bracket to account for the offset of those mounting holes with the S40 mounting holes.
I have a catalytic muffler and have been running it for almost 3 years with no ill effects and no bluing of the pipe at all. Try not to get a catalytic if you can, but if that is all you can get in your area/country don't be scared of it.