If you want a custom exhaust, talk to Jason at:
BSM Exhaust Works & Hot Rod Service, Performance Exhaust Specialist.
The web site implies that they do only American Muscle, and that probably is a lot of it but I broke him in on my VR4 last year. Nice guy and knows his stuff. He re-flanged the end of my Borla to 3in to match the Random Tech cat and did an excellent job.