Need some help

I started out to replace the drivers side mirror on my '70 Dart Swinger. I took off the handle, window crank and panel. I started to take off some bolts and the next thing I knew, I had messed up the lock mechanism. I gold piece with a hook came off and I'm not sure which way it goes. Does it grab onto anything?
Also, how do you get to that nut and bolt on the mirror? I got my hand up there and felt a nut on a rather long bolt. Is that the only way to get that nut off?
Thanks