Thanks for the information. I plan to pull them & do some re-con; replace with new bolts & hardware,, piston seal kits, etc. Deep clean them & re-install with the new drilled/cut/zinc coated rotors. Was weary of 'what' kind of coating might hold up on these, as I can't find a cooperative powder-coating shop here. They're all old-school - frames, large objects... They don't want to mess with smaller parts or finer details like protecting the threads/inner cup for the pistons, etc. So they'll end up screwing them up, I have no doubt. Weary of any kind of paint... I landed on this after I asked what you used, think I might try it. It's a hardcore epoxy coating that's brushed on yet cures to a smooth finish w/o brush marks.
http://www.g2usa.com/
http://www.g2usa.com/