There is a low budget exploitation flick from 1973 called "Group Marriage" that features a '71 Challenger convertible with '72 grille and taillights. Car has a flat hood but rear valance has dual exhaust cutouts. Car has several minutes of screen time. You can watch it for free on YouTube.
Looks kinda weird from the front .....I like it from the rear. Definitely some skill and craftsmanship went into this build. Read somewhere that this was done back in the mid 70's.