When painting any engine do not paint the area the starter bolts to. Here is a picture of a two stroke engine and the area left clean for good ground contact.
You leave this clean so there is no current loss for the ground circuit. I have seen this a lot and We fight this in our shop almost daily with ground issues on modern cars. Same holds true for vintage ones. Working in a transmission shop since the late 70’s this problem has always been around. What people forget is the best ground in the world is the one that occurs when your starter drive gear gets a fresh bite into the ring gear EVERY TIME YOU START YOUR CAR! We see bearing failures in both engine and transmission for this as well as shifter cables welding together and all sorts of issues. On some vehicles if you remove the flywheel cover and crank the engine over in a dark shop it will look like the 4th of July with all the sparks flying! We lightly sand every single transmission case where it matches the block too for better continuity.