I had to remove both trim pieces to replace the rear windshield on my 85 a few years ago. Look up instructions in the FSM for rear windshield replacement..... the steps to remove them are in there. I do not remember the details of removal but here are some pics from spares removed from a parts car.
As for A,B,C,D pilars and why they are called such, I was never sure and looked it up. Looks like it is alphabetical from front to back. If a convertible, or a car with no pillar (all glass) between the 2 doors, the B letter is skipped.
https://en.wikipedia.org/wiki/Pillar_(car)
A, B, and C Pillars - 25 Car Terms You Need To Know | Complex