I spent over an hour using penetrating oil and a torch heating the nuts up cherry red and succeeded in removing all but the last three. Like you, I couldn’t keep the bolt from turning so I used a angle grinder with a cutoff wheel to remove the rest. Where the rear fender bolts to the running board, I found clutch head machine screws with square headed nuts. There was no way those were coming apart so I cut them off too.
I ordered a new set of running board bolts from Classic Parts for only six dollars. In retrospect, I should have cut them all, as I wasted allot of time removing bolts that were too corroded to reuse.
Here is a link for those
bolts.
