At the factory, the screws cut thier own threads, so they removed the paint and had a good connection. With restos geting done, the best thing would be to weld up the original holes, and let the threads cut them again. The next best thing is to srape off the piant under one ear or something, to it grounds well. I also always use some dielectric grease to seal out moisture at that point. Otherwise, it will rust again. That's the same grease you get with spark plug wires...