The K code mustangs were different in so many ways . The K code engine was out of the Fairlanes and comets then into the mustangs . Carby,dizzy, rods,rod bolts,solid lifter cam, heads ,more compression ,exhaust manifolds ,balancer and a better crank shaft . Then the whole drive line inc a 9 inch LSD diff ,then the suspension and exhaust . So an A code was just an up grade from a C code and the K code was totally different and that's why shelby turned the into shelby GT350 mustangs . Ford did well building the K code .