Years ago, I sandblasted the crankcases and gearbox shell that are now in the SS clone. I have to say, it's remarkable they've never oxidized despite having no protective coating. the finish has weathered somewhat, but no oxidation. I'm assuming the blasting peened down and closed the pores of the alloy otherwise the parts would have turned chalk white from oxidation.
That being said, when I needed to clean up the head of the Titanic, I had it vapor blasted. Cleans without altering the surface finish. A slight lapping of the valves was all that was necessary, mostly to check the contact areas.