Pretty much any brand will work. With the mufflers right under the driver's seat, you'll be crushing one every so often, so don't go whole hog and drop a bundle on them. On my jeep, I bought a collar that fits inside the end of the header, bought a reducer to go down to a generic turbo muffler, and then welded the two reducers together. I have my muffler clamped on, and there is a flat 1/4" steel bracket under the muffler protecting/supporting it. On the back end, you can either route it out the back (and lose some benefit from fenderwell headers) or you can just make a short muffler pipe with a 90 degree bend and route it out the side in front of the rear tire. Just hit the local muffler shop or NAPA and check out a catalog. Finding a muffler that will fit dimensionally will be easy...try to find one that is as thin as possible so it will be tucked up higher.
Trying to come up with a witty line to end all of my posts...