I've used Eagle 1 'Chrome and Wire Wheel Cleaner' on bare cast Aluminum with pretty good results. (Credit Chad Blomberg for the tip.)
Most recently used it on a pair of WCFBs and a vintage Dual Quad intake, and they look like new. As with Ken's experience with the Anodized Grille, I'd be careful since it's a corrosive formula. I sprayed it on, let it set a few minutes, then scrubbed it with a toothbrush before rinsing.
May be close to the same formula Ken recommended above.
