Maybe I'm on a different page. The threaded shaft of the shock comes through a hole in the inner fender, then there's a series of washers and rubber rings and finally a nut or two. I don't know that there are any bolts involved up top. If you're sure you're working on a bolt, maybe a picture will help.
If it's a nut, maybe it's the wrong nut for the threads. I doubt that's the case since Bilsteins come with new nuts (or am I dreaming again?). Can you loosen the nut? You might try holding the shaft of the screwdriver with Vice Grips for more leverage.
81 300SD ... buy me