I have used Mothers but get faster results using "Wenol" it's a paste much heavier than mothers. It gets really black when you work it hard, blacker the better. You can purchase buffing cones for your drill (higher the RPM the better) from Eastwood. I have done the rims without sandpaper but mine may not have been as bad as yours.
Here's a pic of the cleaned up rim. Boy I had one heck of a time posting this, may have been harder for me to figure out how to post it as compared to cleaning it...actually my daughter posted it for me
OK check that. I keep on getting an error msg.