If the original parts were anodized then this has to come off as well. Caustic soda solution (DANGER, BURNS FLESH) will do the job but Easy Off (or similar) oven cleaner is a tad safer. Both methods are messy.
Use the wire wheel on a drill or the bench grinder (I use a drill press) to remove all the paint, corrosion and other blemishes. Be careful on aluminum, as the wires will leave deep grooves which you can see in the picture if kept in one position for too long. If no wire wheel is available then use coarse emery cloth which in all honesty will do a better job but take longer. Read more: POLISHING BIKE PARTS FOR EXTRA BLING.