it's not a challenger. but i had a 71 cuda project car that didn't have ANY numbers stamped on the body. no numbers on the cowl or radiator support. the front end sheet metal was original. the car had a 70 rear clip, sectioned in the middle of the doors and windshield pillars, welded on sometime in it's life.
E-bodies don't have numbers stamped in the trunk rails.

perception is 90% of reality