Degrease thoroughly, Walmart brake parts cleaner works well. Heat the parts in the oven at 125* (low) for 30-45 minutes, & check for dark areas,indicating oil seepage. Repeat until clean. Sand blast your parts. DO NOT coat sear surfaces.
A better airbrush won't clog as quickly, but "any ol' airbrush" will do.
Too many coats will cause galling, and may bind. I average 2-4 on any given part, spraying lightly.