"new" 1969 Barracuda

Welcome! Nice '69. Build it the way you want it. Numbers matching isn't important when it's a 318 or slant 6 like the others said. Keep the original drive train aside just in case somebody does want it that way if you ever sell it. Most of the guys build performance cars from the non Formula S Barracudas. So you won't hurt the value at all, and actually make it more desirable.