Try this stuff
 

Busch Aluminum Polish is the best. Look it up on the web. Used by truckers on wheels and fuel tanks. I used it on a set of wheels with great results after a professional refinisher could not do anything to help. Helped my daughter bring home a 3rd place trophy from Carlisle Truck Nationals

Look on Eastwood's website. Metal polishing has a very different set of products than are sold "over the counter". A previous post mentioned jeweler's rouge which is what I use with a 1/4" buff mounted on a drill or a die grinder. They sell kits with all kinds of buffing stuff for stainless/aluminum.

if it's the first time polishing...electro-dip polishing will save a lot of elbow grease.

I don't have much to polish on my boat. However my drag car has quite the engine bay. Jewelers roughe works wonders, but it comes in all kinds of compounds. "White Rouge" is what you want to use on alum. you can even go back and clean it up with the spray and wax that they sell.