Those look like Mac headers. I have those same headers in black and I went with the 12" reverse cone muffler, the same as the one in your link from cognitomoto, except I ordered it direct from Cone Engineering. It may be cheaper that way. The only thing you're missing is the middle section that connects the muffler to the headers and has a slight bend. I'll post a pic so you can kind of see what I'm talking about. I'm sure you could have a muffler shop make something similar?
The 12" cone muffler sounds great, but it's pretty damn loud. I'm contemplating buying the "quiet core" muffler, also from Cone Engineering, to help with noise and to add a little backpressure. The 12" one is 2 1/4" all the way through and provides zero backpressure. It has good top end power, but seems to lack in mid range grunt, although it sure has a nice deep growl when you roll on the gas.
