67 Dart windshield trim & gasket

Hi... advice and suggestions. I have a 67 dart that I am in the process of installing the windshiled and dash. There is a huge opening at each end of the dash between the windshield piller and the dash. I have 68 trim and clips. Help me understand why the gap is there and how do you handle it if you are changing trim? Also, would a 68 dash fit and fill that gap? Many thanks.... Eddie