I painted mine with caliper paint ten years ago. No primer, just cleaned them up a bit and painted them with a brush.
Couple weeks ago I decide to do needed maintenance so valve covers came off. The paint had started to chip in places and small leak of oil as well. SO,
new spark plugs, coils and wires, oil change.
1. Bought a cheap sand blaster at Harbor Freight. Using fine glass media I blasted the old paint off.
2. Ground and sanded corrosion spots and the casting marks. You can use USC All-Metal if you want to fill each blemish and get it completely smooth before primer.
3. Simply paint from auto parts store; Rust-Oleum engine primer, color coat and clear ( 500 F degree )
4. I just got them primed Thursday. went over them with fine Scotch Brit pad to knock down the roughness of sand blasting. Roughness still there somewhat but not all that bad. Waiting to be certain completely dry before continuing with color coat. Have laid them in the sun on concrete patio to help the complete drying. I'll be color coating with Ford blue on Monday the 12th.
5. Have no idea how long this paint might survive! Time will tell, but if I do it again I'm going to use C series Cerakoat.
PS those little screws plug the thread holes when spray painting.