I would remove the rust with a chemical rust remover (Loctite makes a really good one). If you feel safe going more aggressive, you can use a sanding pen (600-800g), or 0000 steel wool. Remove as little material as possible. Then apply some Oxpho-Blue to just the bare metal areas. Dab it on with a Q-Tip, if the area is just scratch sized. If larger, use a small rag. This finish isn't cheap, but will come the closest to a parkerized finish. The good thing is that you can resell the Oxpho-Blue to a gun restorer/builder and get some of your money back. Good luck with the project, and keep me posted!
