I have a 1940 Buick Super. I need to remove the master cylinder to rebuild it, but the bolts turn in the frame when I try to remove the nuts. There is some kind of metal cover over the end of the bolt and no head to grip.
If you have access to the nuts on threaded studs, you can use a nut splitter to get the nuts off. Then you can clean up the threads, and you might have access to the blind side of the mounting point.