earlier shell (red)
later shell below (black)
From my observations , the wider opening was around by early 1974. Yet some early 74's can still have the narrower opening (they can be either way). The later shell (with wider grill opening) has another detail difference , but the width of the opening is the main difference. What I have been trying to ascertain is if any wide opening versions were actually used in 1973 MY production. I have seen some on a few cars , but none known to be original to car. Mostly restored cars.