Heater core isn’t fitting in Plymouth Duster

Dakota Smith said
I accidentally got the one without AC and took it back and they gave me this one and they said it was the right one for my car. I think I’m going to take a dremel to the box that the heater core goes into, so that the pipes fit in. I think that would work.

In your original post you say the car is without AC. In the above post you say you "accidentally got the one without AC and took it back and they gave you the one you have now." If both those statements are correct, you have the wrong core.