I did the exhaust at a custom shop. I designed it, and they mandrel built it to specs. Its T304 and T409 stainless steel, all 2-1/2" pipe, tig welded together.
Dont know about emission legal, as I started with shorties/offroads. Now I got longtubes/offroads.
See these links for MANY photos:
http://www.dariusrudis.com/mustang/suspension
and
http://www.dariusrudis.com/mustang/alternativeauto
p.s. THe only drawback is that with the subframes, I had the pipe go under and around, which is EXTREMELY low ground clearance. Like the width of 3 of your fingers (no sh*t) it was 2-1/2" off the ground and scraped on most everything, when I ran 245-45-16's (short tires). Going to a 17" wheel with 275-40's gave me another 1" diameter tire, so that gave me another 1/2" ground clearance. Tolerable, but not "friendly"...
I might redo it this winter. BIG project to install thru-the-floor 2x2" frame (remove subframes) and then make it out of oval tubing. Maybe.