Do have any plans for the old mast or is it scrap?

If it's scrap I would use a chop saw or sawzall and cut the sections with the parts you need. Then cut those sections to access the back side of the screws. Grind, chisel, break or whatever works to remove the part of the screw on the inside. Take a punch and drive the screw out. For that matter you could just grind the inside surface until the part falls off or some other variation of destructive behavior.