You can wire wheel those parts with a Dremel. I like the idea of the coating. More info? An adjustable rotor for proper phasing is one way, or just make your own locating tab in the spot you need it after you dial it in.
Rust is caused by moisture in the air. By the time I was close to finishing my chassis, surface rust was working its way across the earlier installed bars. If it's a drag car or weekend beater, maybe removing the cap and throwing a towel over the distributor would be a good practice. I have also seen that from engine vapors backing up through the shaft if there is no pcv system on a street car.