yep, if you wanna use some sandpaper on it, I'd use some 400-600 just to do the inside of the corners. Thats where the aluminum is usually the roughest since thats where its bent at.
use a clean rag to put it on, rub it in a circuler motion and then use a different clean rag to whipe it off. Do small area's at a time. Don't try to do the whole thing at once. I usually do the same area 2-4 times or until I think it looks good enough
never used mothers for polishing i assume it can be done. if you have a dremel or a drill od some sort. get some cleaning rouge(brown and high gloss rouge(green or white) and with a polishing pad hooked up to your drill put the roughe on the pad and buff away. you will get a mirror like polish finish. stuff is cheap. rouge is like 4 buck at lowes and the pad is like a buck or 2. start by sanding it down with some high grit sand paper the start polishing with the rouge and it will look good. if i can when i get off today i will post up some pics of one of my shee motor mounts i just finished.
i was told that there is clear coat out there that you can put on steel to help keep the polish and save it from rust. i havent looked for it yet but i will be soon.