Yes, they were both stock cars, but it seems you failed to recognize that the Charger Daytona and the Superbird are two totally different cars, you make it sound like the Superbird is just a carbon copy of the Daytona. When they enforced engine displacement regulations in the late '60s, the engineers over at Chrysler decided better aero was the way to go. The Charger was made for Mopar a year earlier than the Superbird, and Plymouth basically smoothed out what Dodge did the previous year. That's all there is to it.