I used to cheat and run just resonators on a couple of my old street racers. Pulled over you could rev to about 3000 or 3500 rpm and they sounded like a stock exhaust behind a hemi.
Over 3500 rpm they were indistinguishable from straight pipes. Even had the Mopar logo stamped in them from when they put me on the lift to check.
Could anything look more innocent than this car?