Does the Blitz Nur Spec R come with a resonated midpipe / main cat replacement in the U.S.? Can the stock cat be swapped back in and used with the catback part? Is the pipe the same diameter all the way through the mid pipe and catback? What other differences are there between a NUR Spec R and regular NUR Spec? It seems the US Nur Spec R is different from non-US Nur Spec R. Any enlightening would be appreciated. Thanks.