is it the typical Ford "peeling off in sheets" of the late 80s and early 90s? if so, if you have compressed air, use that and a razor blade to take off as much as you can in big sheets. then sand whats left to remove and gouges you made with the blade and prime it. Id use an Epoxy to seal it up. Anthing else wont last long.
i would just sand it down and not waist your time with peeling off stuff if you use 400 grit it wont take long ti get down though the paint. then seal it with an epoxy primer like stated above or a fill primer so its thicker and you can and it and not worry about sanding though it
Get a compressor if you dont have one and use a blower and a razor blade to pop most of that off. A ton will come off very easily, and youll be les likely to hit the bare metal like when you would sand it. If you can, get some plastic razor blades from a paint store and some metal ones. That kind of peeling usually comes off fast like that. Faster than sanding. Afterward buzz it with some sandpaper then prime it till you are ready to paint.