75/76 Duster Grille in a '73?

Darts are the ones don't switch out as easy as Dusters
73-74 Grilles are different than 75-76 Grilles
The major difference is the header panel you need a 73-74 Header Panel to use 73-74 grille and a 75-76 Header Panel to use a 75-76 Grille and the headlight bezels are different as well
But the headlight bezels interchange but 75-76 has more lines in them to match the more fins the 75-76 grilles have

Header panel is what most commonly refer to as "The Beak"