The Rustoleum's "engine" spray paints (500 F) have a primer, so must be useful. I also bought a cheaper brand 500 F paint at Harbor Freight on sale. On my 273, I used Rust Destroyer spray primer, because it claims 800 F and both converts rust and etches bare metal. Even after wire-brushing, I still had some surface rust I couldn't get rid of. But give it >1 week to fully dry since it likes to lift top-coats.
On my cars, I paint the block one color and other components different colors, when I have them off. That gives a resto-mod look. On car shows, they usually assemble everything, then paint it all together, as the factory did, especially Graveyard Cars does so. Your car, so do whatever pleases you.
