The go wing and front spoilers would be organisol, the rear tail light panel argent and the front grill panel body colored, if you are going to make it "most factory correct" for a '73.
You could modify this approach and make the back panel organisol, but the grill just wont fly that way. Because it is one piece with the fender trim pieces molded in to it, the grill is supposed to be body color. You could mask it and spray both colors, but that would be further from correct than the parts your already adding. But that is a perosnal choice. The Challenger in my avatar has a blacked out grill with body colored trim, but it has so many other items that are not original, I prefer it.