I think the simichrome comments are dead on .... I used that on my alum rims and it brought out a color of its own that was absolutley *****en.
http://www.jalopyjournal.com/forum/showthread.php?t=97179&highlight=polishing+valve+covers No ifs and or buts here. Take it to the next level. HAMB professional 'polisher' has some pretty good pointers as well. And I ordered some of his high end polish material to see how much better it is than those ammonia based common polish paste ie Mothers.
Just did an old Cal Custom 10-10 scoop /now air cleaner. Started with 400- 600-800 all with dishwashing soap as a lube. Then I used a mild green scuff pad with mothers aluminum polish followed by a grey pad again with mothers. Then a light machine buff and more mothers on a shop rag, Good enough for me