The "notchback option" with respect to the Duster was the Valiant.
The 2 door notchback option to the Demon or Dart Sport was the 21 or 23 body Dart or Swinger.
A "29" body can be a fastback or a rear window modification as mentioned above on the Challenger SE.
72-74 Chargers were 21 or 23 body cars except the SE which was a 29 body.
Same roofline but radically different rear side window treatment.
