As a guide on how to design a muffler I dug up these pics. When this SM was two days old I cut the muffler open and "de-catted". The results were very satisfactory, but as I said before I like my bikes quiet.
While the mufflers were cut open the baffle design was visible. It's hard to see, but there are three baffle tubes separating the muffler into two chambers. After that the exhaust flows out one tail pipe. BTW, that thing on the right is the catalyst. I was surprised how small it was.
My objective is to package a similar design into this space.