As for the grille, the black sections are actually the natural plastic. If you are patient, you can carefully remove the textured argent from a non-R/T grille and wet sand/polish the black plastic to an original finish.

Otherwise, use a nice satin black trim paint such as SEM or Mar-Hyde for both the grille and headlight bezels.

Note: on the R/T bezels, the black paint should cover all the way to the pinstripe, there should not be a shiny strip visible.