Regular methylene chloride stripper should be fine for the paint. You can use Aluminum Jelly to deal with the corrosion spots.. Naval Jelly isn’t recommended for aluminum, but it has the same main active ingredient as Aluminum Jelly (phosphoric acid) and the same nominal pH (~2.0).

Is the metal beneath the paint plain, shiny aluminum – or is it dark grey, like the engine cases?

Been meaning to ask about that.. I’ve assumed the dark grey is from alkali passivation, but would like to know for sure. Anyone know?

Glass beading is probably best to remove the paint and corrosion leaving the bare metal ready for a self etching primer to be applied. Glass bead doesn’t damage the metal such as sand blasting can do.