I have experimented with removing the argent silver and the body paint that can be on these before. What I found that worked the best was using #2 steet wool and laquer thinner. I know it sounds crazy, but you won't ruin the plastic. The fast evaporation actually works in your favor. Starting in a small area, dip the steel wool in the thinner, let the extra drip out, then gently rub on a small section. It is a P.I.T.A. to do and it takes time, but you will start to see it cut through the old paint. After is softens the paint, keep wiping with a rag. Small sections, light rubbing and patience is the key.
Here is a picture of a 71 Cuda grille that I stripped. That grille wasn't mine and I'm still alive, so I guess it worked!
Hope that helps.
Slotts