Andy, I am still trying to research this topic, but have not made a lot of headway. I am almost certain that the "Special Décor" grilles were either Satin or Flat Black, and not Gloss. The few archive photos ,that show the grilles, seem to show very little sheen.
Was the low mileage red one, that Chad L. had for a while, a Special Décor? If so, that would probably settle the question.
About the rough red one that I have: the black on the grille is so weathered, it is hard to tell on the grille, but one thing that is interesting is it looks like the factory actually sprayed the grilles black after they were installed on the tub. The radiator support is partially sprayed black (all visable areas when the hood is closed is black so you can't see red behind the black grille) and you can see the ghost image of the grille on the support. This paint is original and in better shape (than the grille) and it is satin black ..almost flat black, but not as flat as say high temp black or "BBQ Black". The red and black painted radiator support looks almost crude if you really look at it, but Ford was just building another "Bronco"; They didn't take the care that most 'restorers' do today!