The retainers and windows are different dodge to Plymouth.
I just had the fight you are working on now with the gap between the gasket and quarter panel. No wonder they rusted out below there.
anyway,
I tried, adding a thin foam gasket to the quarter panel, that looked worse then the gap.
After a few more tries, I used 3M strip caulk between the outer edge of the galvanized frame and the inside of the window gasket, before I installed it for the ninth time, forcing the gasket against the quarter panel, now I have a nice fit..
Feel free to PM me if you have any questions.
Greg.