Help with 1975 Duster ID

Hello again, My husband bought this car a week ago. We are new with Mopar cars. I like to look for information about the cars we get, through vin nombers and the Tag of the car, but with this one is been difficult.
Any Tag decoder that someone will recomend? Or If someone can give me a hand telling me, with the pictures.
One vin decoder tells me is a Custom, and other told me sport. Not to mention one told me is a Valiant.
I know that the tailight part is not a regular one.