Everything I have ever read says the only Dusters with twin scoops are the Twisters, and Twisters didn't come with a 340.

Were there exceptions that came from the factory that way? I doubt it but maybe.
Were there dealer-installed scoops/hoods set up that way? Probably.
Were most of them put on later by owners? That's my opinion. But the well-done ones really look like they belong there so they relay look like they could be factory. And MANY owners decided to add them after-the fact.