For fine hand polishing, Simichrome is good. Some suggest Flitz, which works very slowly but can give a jewelry-quality finish – I believe it’s intended for fine metals. But either of these are only used once the surface oxidation is removed..
Otherwise, mop wheels with white, grey and/or red rouge are the go-to standard.
Don’t over-polish any parts that are directly responsible for cooling, such as the fins on an air-cooled engine. Polish the edges if you like, but leave rough everywhere else – you want that surface area!