If you mean putting a Coronet bumper and grille on a 3rd gen Charger, been done.
I can't find the picture right now but I have seen it.
I think he just means coronet to coronet. Don't see why it wouldn't work, might need the earlier mounting brackets if you want to suck it in close to the body. Or slot/redrill what you have. If anything you have more room behind the bumper on a 73.