I am not sure as it was about 35 years ago or so. I do not believe the engine was the original, it was reportedly transplanted from a totaled police car before my brother bought it. I think the X I refer to was on the engine!If you're talking about the vin number, All '70 charger vins started with an X. For '70 it was either XH, XP, or XS depending on the model of charger.