I've used rallye wheel argent silver to paint intake manifolds. Since it has a very fine metallic to it, it looks a lot like "as cast" aluminum. I'd imagine on a smooth valve cover or cylinder head, it would look real similar in finish to a road wheel. Since brakes generate a fair amount of heat, which in turns transfers to the wheel, it will withstand some pretty high temps. However, I've got to say I've never seen any engine spray paint that will stand up to year after year of heated intake crossover air. They all eventually turn brown.
I still think a basic flat top valve cover with the Challenger or R/T badge on it would be easy to do, yet different enough to catch attention.