I did the grill in my '71 with a "satin black". Not sure if it is correct or not but it turned out pretty nice.

You can see it on the website below.

Or here is a link that will take you straight to the '71 Chevelle page
http://temp.corvetteforum.net/c3/dwaynes69bb/71Chevellepageupdate.shtml

 

The correct paint and shade/gloss is SEM #15013 Landau Black. That is the correct paint for plastic and it is dead on for gloss and color.

 

Painted my 71 Grill with SEM Trim Black. Looks great to me