Multi stage wet sanding with wet/ dry auto sandpaper 3M preferably, starting with 800, then 1000 ending with 1500 or 2000 to eliminate fine scratches then some Mothers aluminum polish to finish. I usually have about 2 1/2 to 3 hrs on the clutch cover over couple a days span. Keep plenty of clean water on the area your sanding. That's my method there may be a quicker process,that's how I used to polish the early aluminum frame cr 250's.

 

My boy's '88...soon to look VERY different...