Engine clean up time

When you're painting enamels like Boomer said he's using than all you need to do is complete a very good degreasing /washdown and the alkali in the enamel will self etch and adhere to the existing base enamel that your spraying or brushing over. The enamels are relatively soft and will yellow over time and will degrade. If you have the time and inclination than degrease and washdown the motor, Tape off with good 3-M tapes and masking paper / alum foil where needed and then use a non sanding epoxy primer (any brand, doesn't matter as long as its epoxy) on the entire engine than you'll be able to topcoat with any polyurethane of your choice like Awl-Grip, Alexseal, Jotun etc. Much harder coating , non yellowing with exception of turbos etc , An all around superior coating with less degradation maint. & shine wise. Two part polyurethanes are now being manufactured in "rattle cans" that have advanced spray nozzles that provide a professional job so the need for conventional HVLP rigs and difficult mixing calculations are alleviated .

Z-Spar 100 -G gloss White will darn near stick to a puddle of lube oil. Might have a fish eye or two but it'll stick! Prime any bare metal and convert any rust with Ospho. Wipe down large components and parts with a prep solvent prior to painting. Petit , Z-spar or any auto paint store make / stock a good generic prepsolve for this .

It will come in quarts and gallons. Use a "Pre-valve " for spraying. I don't recommend attempting to brush coat an engine. Pre valves are very good for getting into tight corners and will give you professional results on any surface. A large Pre -valve bottle and charged atomizer will cost around ten dollars and two should be enough for one engine and gear. You will use a gallon between both motors, gears ,mounts and engine beds in my experience.

Cat has White . Water cooled or jacketed DD manifolds yes, otherwise its barbecue grill paint for manifolds.