I used to run M/T valve covers painted like that. Pretty easy to do, just tape off the areas outside the ribbed section. Then spray the ribbed area and let it dry so it is no longer tacky. Finally, stretch an old diaper dampened with solvent tightly over a sanding block, and carefully wipe off the tops of the ribs. You might need to do a little finesse work with a Q tip moistened with solvent, but it is really pretty easy once you get the hang of it.