if the parts have scracthes in them use wet/dry 220 paper(or finer) to sand them out, then polish with jewlers rouge compound. i use a bench grinder with a soft polishing wheel on it. i make large scale car models and use aluminum for engine parts, exhast, rims, basicaly any and everything. parts come out smooth as glass, and shiny as chrome when done rite.
if you want ill post pics of the ones ive finished, rite now im building a '63 corvette pro mod dragster. bout 3/4 done