There are no stupid questions, only stupid answers.
But Terry and Moparleo are correct and wouldn't steer you wrong. There were no billboards for Challengers. One of the major differences between the Challenger and the Barracuda is what's referred to as the "Belt Line". On the Barracuda the belt line is straight and stripes, belt moulding and the 71 billboard looks nice on any year E-Body Barracuda. The Challenger belt line sweeps up in the rear quarter panel and the line itself is more "pinched" for lack of a better term. Stripes and belt moulding look cool. But with shadowing and reflection on the curved surface of the Challenger, I personally don't think a billboard would look all that great. But hey, it's your car and you can put what ever you want on it. With the sweep and pinch, I'm pretty sure you'd have to paint on the billboard.