You could waste your money on a stealth system for the 'spec' but it wont make any difference.
I think, providing you would keep it impeccably clean, any of the stainless steel group N pee shooters would look good, like an oreca group N, or a kam racing supersprint. I suppose a powerscrap place could probably make you a custom back box for less that would look similar but still be quiet.
Just have a look at the back of some sports and see what you like, afterall, that looks pretty similar, just minus the side skirts.