On the factory as well as the Stromung exhausts that I have had, the center section is interchangeable between B13's. The rear section has different bends, lengths, and hanger locations.
If you already had a good center section you might save a couple bucks by only having to fab a rear section. I did this to mate a Stromung center section to the Nissan Motorsports (Borla) NX rear section once and it both looked and sounded good.