I can tell you, I had a factory 74 Duster 360 4 speed car. I sold it for $3500 40 years ago. It was a super nice original car. (For the most part) To this day, I regret selling it. You have a VERY rare car, especially a sunroof car. KEEP IT! Return to stock appearing, hop-up the engine a bit, (It won't take much) & it will run pretty damn good. Mine still had the factory exhaust manifolds on it, mild engine work as in a little larger cam & that's it. High to mid 14s with street tires. It would run. They were as fast as most any 340 car.
They don't get the respect they deserve because most people think they are smog era cars, WRONG! Keep it or you'll most likely regret selling it one day. It looks like a pretty