I used scotchbrite pads, thinner, and elbow grease to remove the argent paint from my grilles. Wasn't previous owner though. Factory painted portions of most grilles.
Just a plain ol' SOS soap pad and lots of scrubbing will bring it down to a nice smooth shine. I don't have a close up of my grilles in a digital format to show you, but I did the hood inserts on my 68 Fastback in the same way.