clean cast iron, spray with a few heavy coats of gold galvanizing primer, then two coats of rustoleum apple red. Beginners. 500 and 5000 miles respectively. primer still shows on the headers.
I have measured the temp all over my engine just for kicks using an infrared thermometer. That part of the heads gets up around 450-500 degrees F. If you can find a paint to withstand those temps, then maybe it would stay on. I think regular engine enamel isn't stout enough. Exhaust cross over on the intake gets up around 250 F, and the paint on that part of my intake looks crappy now also.
I think the zinc primer helps insulate against "parent heat" transfer. Color in spray paint is merely plastic in a clear "vehicle".
