I read that entire article and this is what I found:
First post, 4th paragraph, "I am sorry, but I can not remember if GM used a flat black or not. I think they did, but I used a gloss."
First post, 11th paragraph, "Some people do not like it, But I used a gloss black Plasticote paint..."
Reply number 7, "The paint looks like flat black and just covers the flat ledge surface and stops before the lip of the ledge."
Reply number 29, "went with the flat black..."
All of these posts either say what they think is right, or just what they did. I just want to be 100% sure that the flat black is the way to go.