Painting plastic can be tricky, it depends on so many things. That said, I did once paint the air/heaterbox on my Torana years ago, I just cleaned the airbox really throughly and used el-cheapo matt black, it came up fine, gloss may have looked better, I dunno, but of course, once painted it will never look original. That said they do tend to discolour, I can imagine many owners paint them. A good second hand one is probably around 100 bucks.