Upon replacing the distributor cap and rotor on my 60 the bolts that held down the old cap were so rotted when i unscrew them they snapped off. So 2 of the 3 screws snapped. Now i can't bolt on the new cap and i am in a dilema. My 60 is my daily driver. What's the best way to remove the remaining screw part that is still in the housing part without damaging the threads for the new cap?