fla3006,
You will likely have to make,or modify,a screwdriver for these screws. My German gunsmith friends made all their own screwdrivers( in old days, this was part of their training).Also in "clocking" these screws, they filed or sawed the slots themselves.Therefore, their own screwdrivers fit their own screw slots.If filed, the slots were often "v" shaped and easy for ill fit blade to slip out of( they were careful), if sawed ,not so bad.
Mike