Is it a Dodge or Plymouth?
I have, what i believe to be, a 1966 Valiant convertible. According to the vin # it
should be a dart but all badges indicate Valiant custom 200.
How can I determine if this is real or something someone built?
Plymouth Valiant, Dodge Dart! It would be a huge amount of work to turn a Valiant into a Dart. Post the VIN and maybe we can figure it out.