If you look closely at the Dodge Challenger and the Dodge Charger side view, the top of the fender on the Challenger has a tighter radius curve at the front of the door than the Charger (same as Magnum). You would need to either fit a set of Challenger doors (porbably not possible) or cut the front off of a set of charger doors and a set of challenger doors, and weld the Challenger door front to the Charger door front to make the fenders ftiproperly. The other waqy to do it would be to cut part of the Charger fender sheet metal off, and also cut off part of the Challenger fender off and then weld the rear curved part of the Challenger fender to the Charger fender. In either case you are looking at a lot of metal work.
The new style front fenders of the Charger look like they might fit the first gen Chargers & Magnums, but the Challenger looks totally different.