For cast iron parts, I first soak in evaporust to see how they turn out. Sometimes they are good enough to put a protective coating on and use as-is. Otherwise, blast with glass bead, nothing too rough that etches the surface bad. Once they are clean, do a quick 15-30s dunk in manganese phosphate. This will darken the metal just enough so they don't look like they were just blasted. After that, soak in oil for 24 hours, wipe/clean and install.