That's trickier. The grille can likely be made to fit the fenders with some new holes or additional brackets. And the hood should line up and the hood support/latch panel should still work.
Where it gets tricky is the bumper and lower valance, and possibly the headlight trim. The '74 Dart fenders have a different relief for the bumper, and no way to attach the valance used on the '70-'72 cars. So that would require fabrication and some body work for sure. Not sure about the headlight trim either, as the '74 fenders wouldn't have a place to bolt those chrome eyebrows. None of that stuff is impossible, but from a time and money perspective it would probably be a lot easier to buy a set of '70-'72 fenders.
It's easier to convert the '73+ Dart fenders for use on the '67-69 Darts than it is for the '70-'72 body style.
