Lots of incorrect scoops have been put on Dusters either by the dealer or owner. The dual snorkle scoop did not come on any Duster. The Twin scoops only came on Twisters. No scoops came on any year 340 Duster. Who cares? Unless you are going for an absolute original restoration, do what you will like the most. Most people won't know or care if it is wrong.

Edit: I would not consider it 100% impossible for a 340 Duster to get a wrong hood treatment while going down the assembly line. You never know. If it did it would not be on the window sticker, build sheet or fender tag so impossible to document.

If a cash customer came to the dealer and said I want that 340 Duster but I want the hood from that same color Twister next to it you can bet that in about half an hour there would have been a 340 Duster with scoops and a Twister with a flat hood.