74 duster seat-belt bolt not coming out

Hello,
I have a 74 duster with a 3 point harness. Im replacing the belts but I cant get the bolts on the roof off from both sides. The bolts just spin, I do notice there is a slit below the bolts. I tried to shove a flat metal bar in there but I didn't feel anything as I spun the bolt.

How have you guys and gals removed them in the past?