America's favorite pony car turns the big four-oh on April 17, and the GT-R is its mid-life crisis birthday present. Officially it's a concept car, but it was developed and built by Saleen Specialty Vehicles in Troy, Michigan, to be capable of competing as a racecar. It also aims to show grass-roots racers that they can take a stock Mustang (85 percent of the GT-R's body structure is unchanged), and build a competitive vehicle at a reasonable price using parts from the Ford Racing catalogue, like the 440-hp 5.0-liter "Cammer" crate engine that retails for $14,995 and can be tuned to over 500 hp. That power is routed through a Ford Racing TTC-T56 six-speed transmission, a custom metal matrix composite aluminum driveshaft, and into a race-spec 4.56:1 differential. Big Brembo brakes, 20-inch Pirelli racing slicks, and competition suspension (retaining the live rear axle) round out the package. Carbon-fiber is used for the hood, grille surround, and underbody belly pan, and the orange paint is meant to evoke the Grabber Orange 1970 Mustang Boss 302 Trans-Am race cars. Happy Birthday, Mustang...and many more! Click here to watch the Mustang video. Click Here to see photo gallery.