I have a couple of the old springfield 87as and have not seen one with a plastic stock. probably Bakelite, Tennite or some other fancy plastic/ synthetic from back in the day type material. I'd love to see pics. You might carefully remove the butt plate and see what falls out. I'd definitely use a good gunsmithing screwdriver on the screws and maybe give em a shot of kroil before removal to keep from boogering up the screw heads.