Actually, the black paint acts as a pretty decent primer, just make sure to get rid of any big chips or cracks in it. Wash it down with dish soap to get all the old crap off of it and spray it down with water. Next, use an air compressor to spray off all the extra crap and dry it. Spray it with whatever color you want, but make sure it is high temp engine block paint. Spray the first coat, wait 15-20, spray another, wait 30, spray another, wait 30, spray the last and wait about three hours. Bolt it all back on, making sure that your old valvecover gasket is still good and positioned correctly and you're good to go.