Swap 65 Valiant grill for a 65 Dart grill?

Yes, the '64 Valiant grill will fit on your Barracuda, but then you won't have any front turn signals unless you also swap in a '63 or '64-'65 Valiant front valence with turn signal lights built in. It might(!) also be possible to swap on a '66 Valiant front bumper with built-in turn signals, but I've never tried that.