I painted a pair of old Buick 455 valve covers once, with black wrinkle paint. I spent a lot of time on prep work and degreasing which I think is key, but then I was rather unoriginal and just followed the directions off of the paint can. . lol, though I did set them in the sun to help 'bake' them.
They turned out awesome - I got a lot of compliments on them and they really stood out from the rest of the engine. The paint was pretty durable too, which surprised me - I think the 'baking' helped?