OK, figured out how to get the mirrors off, for those curious:
The mirror is attached with a bolt, washer and locknut. Mine was SO corroded that I had to hit it with a hammer and LOTS of WD-40 to remove the HUGE buildup of aluminum rust. I also had to get a #3 Philips as my #2, the biggest I owned, was starting to strip the faces.
Happily it FINALLY started to turn, unhappily it turned forever. That's when I realized that it was held in by those locknuts. How to stop them from spinning free?
I see them, but I don't know how to get to them. My arm is only so long. I got my vice-grips and I reached as FAR as I could, figured out how open they needed to be and finally clamped them on the locknut. Awkwardly unscrewing and hearing the vice grips bang around. Finally they fell to the ground. One down.
I managed to do it all 4 times but there wasn't enough slack in the wires to put the mirror down when I removed it. I had to re-hang it by one of the bolts and go behind the fiberglass one more time to undo the blue inline connector so I could take the mirror down. There was another wire going into the mirror, perhaps the turn signal? It let the mirror reach the ground so I set it down and tried to unhook the wire, but it was permanently crimped. Got my wire cutters and cut it at the original splice. Will have to put that back when I get the mirror re-finished.