If it's bone stock why does your personal info state it has 437 HP? Just curious...
As far as the exhaust is concerned... Don't want to sound too much like an ass, but this subject has been beat to death in these forums. Too bad the damn search function isn't working!
You said the car is too quite, so do you want to just make it a little louder, or do you want to add some HP & TQ too? Cat-back sound is subjective... ask 5 guys what sounds best and you'll likely get 5 different answers. The most popular choices for the 03/04's are (in no particular order) Magnaflow, Bassani, SLP, and Borla (Stingers). MAC & Flowmaster make cat-backs for the 03'04 Cobra, but make is not well know for their build quality and Flowmaster's seem to be down on power a little when compared to the others. Most all of these cat-backs are well engineered and made from stainless steel (except the MAC or Flows). Choose what sounds best to your ears!
U.M.
Since this thread is more "Talk" than "Tech" I moved it to the appropriate sub-forum.
For less than $100 I put "'glass packs'' 13 inch mufflers that look just like borla's. No problem with clearance-fit. With Bassani catted x pipes great sound and excellent acceleration --- feels like 30 HP increase over previous flow masters and stock mufflers. A little drone at 70 mph but no worse than the FM's.