The 68 nose and doors will technically bolt on to a 66 Charger. The cowl,engine bay and hinge pillars are pretty much the same. You will have to use the 66 vent window frames,and side glass in the 68 door shells to make them jive with the A pillars,quarter glass, and roof line. They should be pretty much direct bolt in. The door jambs at the quarter panels are way wider on the 68. You could change the rear section of the door jambs from the 68, and graft 68 rear quarter skins on the car to achieve the 68 look with the earlier fastback style roof. You would also have to change the trunk extensions and outer wheel houses to fit the 68 quarter panels onto the car. There would be a lot of metal work to make the quarter panels blend together with the earlier style body, but it could probably be done. The next challenge would be what to do with the tail panel and rear bumper. Charger body style was almost scrapped in favor of a fastback design by the chief of design Bill Brownlee, but he went on vacation, and his boss overruled him when he saw the clay 68 prototype in the design studio! Brownlee was furious about being overruled by his boss. The one thing that Brownlee did do for the 68 Charger design though was the gas cap location. He was pissed off,and ripped the gas cap from the center of the tail panel and put it ontop of the rear quarter and said this belongs here. If you do build a 66/68 hybrid car, it will look much more what Bill Brownlee has envisioned for the 68 Charger. The long buttress rear window and fins on the 68 Charger were a compromise to emulate the fastback design of the earlier Charger models. Brownlee was not entirely wrong about the Charger needing to be a fastback design, as we learned from Nascar.