I have done a couple of valve covers for myself as well as friends, I use a light media in the blast cabinet, then different types of polishing compounds, I start w/ the black stuff, then brown and finally white, took me all day, but it looks good.

if you don't mind spending $$, it is about a hundred and fifty bucks to have it chromed..

And for those of you that have powder coated covers, try the stripeeze from your local home depot, it worked for me, just soaked the valve cover in the crap for about 3 hours...paint peeled right off, but beware of the fumes...