An Orphan car is something like an AMC, Studebaker, Packard, etc.
Cars who's original manufactures no longer exist. Kinda like a kid whose parents have passed. AMC is the best example, in 1987 Chrysler bought up AMC to get to Jeep. They wound up with Renault and Eagle as well in the buyout. Chrysler serviced parts for them until supply was exhausted.
But your car is a 67 Dart, it's a nice Dart, I'd own it, but there is no special category other than antique.
