I'm thinking the 79 CS is for stacked quads? Don't see why you couldn't do it.....been a very long time since doing stuff like that. I put a 78 Trailduster grill in a 74 in around 78 and it was a drop in thing.
Well, that's a new one on me! Kinda odd that the centers have a different spacing after all those years. I remember laying the Trailduster grille in my 74 to check the fit and was a bit surprised that it fit so good.