You will find how to remove the trim and everything else for that matter in the FSM. The leading edge of the belt trim is held with a "shoe" that has a stud. The shoe slides into the trim strip and is secured by a nut on the shoes' stud. Access is eith from the fender well with the inner fenders removed or thru the headlamps once they are removed. The rear of the trim is usually held with a visible nut in the door jamb. The trim is held with plastic retainers and will likely need to be replaced. There is a plastic retainer that is inserted into the body, retainers are then slid into the channel, and then lined up and pushed to adhere.
You will need many of these and suggest looking at the Flying Spares website to see what you're dealing with.
I had no issues with the front windscreen gasket from Replacement Parts. The door seals held by a channel on the door with no adhesive.
1980 SWII LRL-41587C FInj
1976 SS LWB LRE-23114 Harkness RR