All 1973-1976 sunroof cars could have either a steel roof or vinyl roof. I know of a few coded for steel roofs like mine. On the fender tag on my Duster it says TB3 for upper body color not the vinyl roof code which is VI* (asterik being a certain letter for color choice) The code for all 1973-1976 manual crank sunroof cars is M52.
I believe the early and very rare 1969-1971 B & E body power sunroof cars all came with vinyl roofs but I'm not going to say I'm 100% sure. The code books state M51 power sunroof/with vinyl top for the 69-71 cars. 71-72 A-body canvas sunroof cars were M52 I believe but of course it was phased out for the manual crank style in 1973.
The Demon in question has had the sunroof added for sure and the car should have a complete personal inspection before anyone buys it or some guarantees that's for sure.
