Sales code V5X denotes Vinyl Side Molding, Black.
V5= Side Molding, X=Black
The molding is as pictured on the Dart or the second Demon picture.
NOTE: Demons, nor any other Chrysler products in the 1970s, had a V-6 engine. The engine in US domestic car and light trucks (excluding late 1970s truck Mitsubishi built 243 diesel six cylinder) are the slant six, or also referred to as inline six, cylinder engines.