Hello ,
I also recently paint my engine. First I cleaned the engine with degreaser and high pressure hot water (attention for water entree) After this procedure I use paint thinner to remove the rest of grease. The valve cover was grinded to bare metall,than I primed the engine with a thin layer of Epoxy 2K primer. The last layer is the original 1K metallic green of the paint what AH Spares sales.
This was my way. No guarantee because I have no liftime experience after hot and cold cycle....
One tip if your engine is out: You should remove and change your engine plugs !
All my plugs were rusty from the inside with a very thin rest wallthickness! It cost low money, and you eliminate the risk of a drainy plug on the engine compartment firewall side.
Also I clean before assembly the plugs, with high pressure the rusty cooling channels. (rust,sand and calcium carbonate)
Bye michel- from sunny germany