[Jdub]

See your Haynes manual: Up to ?June of '79 you have a small pin that will need to be removed from the arm, just up from the circlip etc. Swipe the dirt away and you will see it. (you already knew this).

Drive it out with a small pin or otherwise. If you cannot free it easily then you need to clean the side of the pin that is exposed and drive it back in, trying to reverse course if possible to expose and trim down the other side. Be sure to spray WD-40 in the exposed area. Right now I would guess that the pin is stuck because it is not in the hollow area alotted for it but instead is now trapped by pulling the arm down (or maybe up). Play with it a bit, moving the arm up and down on the shaft.

EDIT: You may also need to move the arm rotationally. There is a good possibility that the arm is holding the pin due to rotation and again the hollow is not "open" to the pin and thus the pin is trapped. Keep at it; you will have this out in no time do not fret!

John