Does anyone like 4 door A body mopes?

how does one know if his car is a custom vs. any other of the trim lines?

If the emblems are missing, check the VIN's first two characters. LL= Dart ("Dart 170" through '69) ; LH= Dart Custom ("Dart 270" through '69). Works the same with Valiants; VL= low trim line, VH= high trim line. There was also a "P" for premium, originally applied to the Dart GT and Valiant Signet. Signet eventually replaced V200 as the name for the high-trim Valiants (even 4-doors), so at that point a Signet was a VH rather than a VP. I don't know if the P trim was ever applied at the VIN level to a 4-door. Maybe the last-few-years Dart Special Edition and Valiant Brougham.