That is a common trick in the automotive world. When I was young and poor, we did something similar. The contact plate is a round copper disc. It had a hole in the center with a shaft and spring to align it. We would drill out the rivets [your starter contacter is held together with rivets] Remove the circlip on the shaft, remove the copper disc and flip it over. No filing needed. File down the contact surface on the copper stud that the cable attaches to. Reassemble, & bolt/rivet it back together. You can use screws & nuts, blind [aka Pop] rivets or solid rivets. If you would like to use solid rivets [for a more original look] I can supply some for free. I've got hundreds left over from my Vans RV-8A project. You have little to lose by taking it apart. Consider it an educational experience.
Charlie K