I think it would impede it more than straight through mufflers. I have to reiterate that my SVT with straight through resonator, and twin straight through magnaflows with headers and a main cat was not too loud, but Just the right mix of rumble and v6 rev sound. At least for me. The guys who liked Rice thought it was too quiet. THe guys who like V8 rumble like it a hell of a lot.
The duratec does have its own distinctive sound when uncorked without being obnoxious.
BTW, how is the car running? Were you able to dyno? How about those top secret mods we were planning from way back when? <lol, you're going to get some questions on this one I promise! sorry bout the publicity
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What about the torque prior to the secondaries opening, and what happens afterwards?
so I have very limited options. I currently live about 1 hour away from Lincoln which has a dyno around 48th and Cornhusker. Sadly, In the next 3 weeks or so I will be moving about three hours west to a town of around 25K. Which ironically has the only drag strip in the state (the other strip closed up last year). So you guys just may have to settle for track times. 
