I would use a chemical paint stripper followed by glass bead blast. I would tape off the sealing surfaces before bead blasting - I like the look of a nice machined sealing surface and the bead blast can dull the finish. If you are too aggressive with the glass bead blast, you can erode the aluminum (glass beads are better than regular blasting sand because the beads are rounded rather than angular, but they're both made of very hard silicon dioxide). I've seen the sealing surface of aluminum parts damaged when the operator used the glass beads to blow away a stubborn bit of sticky gasket.

I've also dipped many aluminum parts in the caustic baths used in machine shops. They will definitely get rid of the paint (or 99% of it) but they don't always get rid of the staining from years of gasoline, coolant or oil on the aluminum. Those stains seem to be impregnated into the metal. Bead blasting after chemical stripping did seem to produce a more uniform finish & colour. The caustic bath was also not very effective at removing the cooked on oil residue in the EGR port. Not sure what will remove that but I suspect that anything that would dissolve that coked oil would probably eat the aluminum too.

Be extra diligent blowing the beads out of the ports and cooling jacket. Those beads can destroy a water pump (or worse).