Wally, you could make a template out of construction paper by rolling ink over the letters on your spare valvecover, then pressing on the paper like a rubber stamp. Cut the inked letters out with an x-acto blade and lay this "bib" over the gray one so the letters fix the location; magnets work to lock it down. Fog some blue on the exposed letters and you're done. It's time consuming to hand cut templates, but if you're doing more than one it's invaluable.
Then again, you may just be able to use a hard roller and achieve the same result. It sorta depends on how thin the paint is and how tall the letters. I'm a "mask and shoot" painter, and have the empty rattlecans to prove it.
