If you're trying to protect the original aluminum surface (assuming they weren't scuffed up prior to the previous paint jobs) I like to use aircraft stripper and a toothbrush. I've had soda blasting done on smooth castings to keep them smooth but I have to farm that out.
A good media blasting shop will have multiple media choices if you've got one locally, I've gotten great work and advice from a place near me, even DIY and blast cabinet advice...he preferred bigger jobs.