The single-headlight grilles were made from cutting sections out of another grille, cutting the hi-beam section out of the headlamp bezels, and overlaying the grille section; if you look at old photos, they didn't line up flush.
Front mag wheels had straight spokes, I think ET makes aluminum replicas.
The more clever, difficult and/or spendy stuff is the RO/WO race interior, RN123 shifter lens, the Plymouth (1" -shorter) wheelbase on Dodges, and the exhaust system. Some had 1-piece door glass. The rarest, most coveted & expensive race piece is probably the stainless K, but there's probably only 1 or 2 left worldwide. They were blamed for what was actually rear axle deflection and they were swapped back to the "production" piece.