Well, i decided to go with a color instead of polish, rather than deal with the headache of clear or no clear and repolishing.
I also did a test of how the magnesium reacts to acetone,
End of the day, two freshly buffed magnesium valve covers, cleaned half of one with acetone, and left the other half untouched. Came back the next morning to find the side that I cleaned with the acetone had oxidized literally overnight. There was actually a line on the edge of where I wiped it, with oxidation on one side and nothing on the other.
So if nothing else, I would say it's advisable to abandon the acetone wipedown before coating. (for magnesium)
Went with amber illusion by the way (hows that for a difference from polished?
)