HOW TO PAINT POLISHED ALUMINUM ENGINE COMPONENTS?

Blast and immediately paint with self etching primer. Or, you can pay to have the parts anodized and left with no dye or sealer to help with paint adhesion. I've never had trouble getting paint to stick to clean type 3 hardcoat. Type 2 can also take paint well.
Bare aluminum will oxidized almost immediately and so prep must be done just prior to paint and the surface needs to be very thoroughly cleaned just prior to paint as well.
Oven cleaner is easy to diy as it can etch and clean and is fairly easy to wash off. Use hot water, blow dry with compressed air and then paint asap.
I'm no paint pro though, these are just things I've done or have experience with - the anodized parts I've painted are anodized regardless, so it wasn't a special step taken specifically for paint.