All we have ever used is Snyders. You want to clean the engine, wire wheel off any rust and loose paint. Simple rule is if it's cast iron it's green, the pan, pulley, carb, starter, fan and generator are black. Some people paint the exhaust manifold, we just leave then natural. If the engine is coated with crud, I have used oven cleaner in the past. But it a very messy job, best done outside and needs to be washed off. The engine paint seems to be more forgiving of a little oil left on the parts. You only what to paint to cover, keeping the thickness of a paint to a minimum.
If you use oven cleaner read and follow the instructions on the can and keep off the body parts as much as possible, don't know if will hurt but better to be safe then sorry.