For that kind of many and plenty of change i would recommend Hayward & Scott
http://www.haywardandscott.com/results.asp?category=13 Hayward & Scott are specialists in the fabrication of custom stainless steel exhausts for numerous road and race car applications.
The company has crafted systems for numerous vehicles including Ford GT40's, Aston Martins, Jaguar D-Types and various Ferrari and Porsche models. Our expertise has been built up over the last twenty years constructing systems for wide range of vehicles, from Austin Sevens to Formula 1 cars.

Subaru Impreza Classic original style Scooby design back box
Original style Scooby design back box, subtle in terms of looks and sound, friendly on the motorways but growls at playtime. Centre and back box on its own will give 18Bhp. Complete de cat system will give 25Bhp.
or

Subaru Impreza Classic Twin outlet back box
Twin outlet back box, still gives a nice deep sound but subtle sounding with the original style look
There's no code as such but I hope these help with your quest, if you want any more help just ask
