Here is a Road Racing video of a Shelby GT500. I think they said the only mods are a catback, tires/brakepads, and cooling ducts for the brakes. This was posted on the corral.

Video - 2007 Shelby GT500 hits the track running at Road America. Taking my Track Dawg for a ride. He coaches, cheerleads and comments on the car and the vehicles we encounter on track.