The correct approach to painting an engine is a subject with strong opinions and a clear answer: use a quality heat-resistant enamel in the correct color, prepare the metal correctly, and apply it to a clean engine, not to an engine with oil contamination.

Engine cleaning before painting requires degreasing followed by etching the metal surface. The etch provides mechanical adhesion for the paint. Paint applied to contaminated metal will peel within months of operating temperature cycling.

The color: most American V8s of the muscle car era were painted at the factory in a specific color that's documented. Chevrolet orange is the most familiar. Pontiac used a blue. Ford used light blue on small-blocks and black on the 390 and 428 FE. Use the correct color if you care about correctness. Any color if you don't.