I have painted valve covers on my 68 YS. I actually had someone say that I was 'mistaken' and the engine was a 350. I asked how he determined it to be a 350; he said painted valve covers. I pointed to the YS and asked his feeback.
My engineless car came with its origional number match intake and origional valve covers, and the covers were rusted lamf. I canned the covers and used the ones off my 350.
Three reasons I use painted covers. First, It makes the engine look ten thousand times better than hokeyass chrome. Second, chrome is, by far, the ugliest thing you can have under the hood, almost looks like something to make up for ED. Three, I have owned the painted covers since 1977.