Yoda approved "cheap and good" aluminum case polishing
(not!)When recovering an old bike with crudded up polished aluminum cases, Yoda taught me to sand the covers with 320 grit wet or dry paper (wet) until I have removed all surface irregularities on the remaining clear coat and blended the edges of the clear coat to the now roughed up aluminum. It is not necessary to sand off all the clear coat, just remove the oxidized outer part and blend in the rest of the edges where the clear coat chipped away.
I then go to the car wheel detailing area and buy a big can of silver metal flake wheel paint. HINT: take a cover with you to help you decide on which of the 10 shades of silver metallic you are going to use.
Using masking tape, tape off the cover from everything else and shoot it in several light coats, building up to a finish coat that is deep and lustrous.
You don't have to take the bike apart if you pick the right tone of silver to match the weathered uncoated barrel and case castings, and yes, you
can paint right over the screw heads if you spray them clean with carb cleaner.
Here is a set of side covers done this way that has over a year of use on it now. Obviously, you can do a better job if you take everything apart, but a perfectly acceptable job can be done with the bike fully assembled. Note that I masked the pipes and painted around them, so that too isn't an insurmountable obstacle.