70 and early 71 were Go wing . Later 71 was a gull wing. 72 was not available with a wing. That lid you have is a rare lid if it has the rib with the spoiler cut outs. I have owned and stripped many and only ever saw one. My opinion is that the gull wing matches the contour of the roof and tail panel of the Duster Demon body style. The go wing was for the 70 Dart swinger , Roadrunner , Super bee , Carried to the 70 Duster but was changed to fit the fuselage body styles for all 71 cars.
You can see this 71 Roadrunner has an After market wing. it has no arch they flatten in the sun and the points are more rounded