Well, I finally got the stuff to upgrade the single exhaust to 4 inches. The muffler is that stainless unit that's available on E-bay. It's a monster. I'll be keeping it a single exhaust (4-inch duals would be way overkill) with exits coming out in front of the rear tire (which is how it is now).

My current exhaust (from the previous owner) goes from the 2-1/2" pipe down to 2-1/4 or maybe even 2" at the muffler and tailpipe. I think it's way too restrictive. I'm sure 3" pipes would have been enough, but the y-pipe is 2-1/4", so the 4" is less than twice the y-pipes. I think that's a pretty good fit.

Anyway, I did some of the first welds tonight and have a few pics posted in my gallery, if you guys are inclined to check them out.