Unfortunately, the AAR version isn't designed to sit under a Challenger with its turn signal pods. It would require some mods to fit.
The MAS version is pretty flimsy and while it will direct air into the radiator, it would require some mods to actually produce down force.
Showcars is the worst fiberglass provider I have ever seen. I would only use their stuff if it is the last available option. Plan on spending many hours cleaning it up.
You could also make your own. Here is my T/A copy made form sheet aluminum