I agree with the wire wheel, plus maybe sandpaper on parts that aren't greasy. If the prep is done right, you can prime and paint like other parts. I have used
Picklex 20 as a rust converter on top of bare metal, followed by
Zero Rust with good results, although some will say to never use these cure all rust coatings. My purpose is to not use them in lieu of good prep work and necessary metal removal, but to protect against surface rust and prevent rust from forming.