After soaking for over 2 weeks in the purple stuff, all the paint finally came off of the spoiler end caps and the fender vents. There was some thick paint on there for sure.
I was also able to trim the black spoiler end cap to the correct length by placing a piece of masking tape along each leading edge of the white end cap and marking where the taper ended. I then removed the pieces of tape and placed them on the black end cap along the same leading edges. I then marked the locations. I then verified that the cut angles were the same as on the white end cap (65 and 80 degrees) through the use of my 7th grader and her protractor. I then used a fine bladed hand saw to remove the excess and voila, a correct 1970-73 end cap.
Before:
And after:
