Front coil spring seats - what is the proper finish?

I'm replacing the front coil spring seats. The MCA judges manual states they should be "natural". But when I received the new ones from Scott Drake they were painted black. Which is the proper finish?
BTW, I already sand blasted them and will either repaint them black with POR15, or treat with gun bluing and Eastwood's Diamond Clear to have them be "natural".

This is on my 1969 Mach 1.
Thanks for your help.
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