The only problem I can think of would be the trans crossmember and the gas tank. The cross member may or may not have the cutout on each side for both pipes to run under. The gas tank may present a problem as well considering I dont think there were and factory dual exhaust cars from 63-66. Even the Formula S Barracudas and the 273 Commando Darts had a single outlet on the drivers side. It can be done, but you may have to do a little modification to the tailpipes. Other than that, its a good kit. I have run many on my own cars over the years, in both 2.5" and 3" setups.