Yeah, the bump stop has a 3/8 fine thread sticking up, with a spring washer and a 9/16" af nut on it. Hold the bumpstop (It might be scalloped away to clear/locate on a rivet head) to stop it turning and undo the nut on top, inside the channel of the frame.
It shouldn't be too much of a headscratcher. A liberal dose of the penetrating medium of your choice prior to attempting nut removal might be a good idea.
Mart.