The 78/79 grill and bumper were very popular upgrades back when they were fairly new. The rectangular headlights were 78 high end trim and 79 all. 78 lower end trim levels got the same grill, but had round headlights. Either style requires the matching radiator support, as the headlight buckets bolt to it, round vs square are different, and are higher on 78/79 than 73-77 since the earlier models had the turn signals above the headlights.
Unless you are going for a totally accurate restoration, the later grill is typically preffered by most people.