I have a Winchester Model 70 for which I've ordered an M*CARBO trigger spring in order to reduce the trigger pull. M*CARBO has a nice video about how to replace the spring and I'm not concerned about how to do it, my concern is which size screwdriver do I need to remove the front and rear trigger guard screws and the stock takedown screw? I do not want to mar these screws. My rifle was manufactured in 1978. Thanks in advance for your assistance!