I don't know about Challengers, but surely they aren't that much different than a Barracuda. My '73's radio opening allowed for the steel cage that most new stereos are mounted into, to fit perfectly. The only thing that I had to do was construct a support underneath, using L aluminum pieces and an aluminum plate, to help hold the thing in. Can't see any of the brackets unless you are underneath the dash. The whole thing is very secure and really a clean install.
Just wanted to throw that out there...................