I will be coating my marine engine with Motor Coater, but have some rust spots on the iron die-cast manifold. How would you recommend I prepare this spot before applying the Motor Coater Engine Paint?

It would be best to clean the entire marine engine with KBS Klean.  Then, you can treat the rust spots with RustBlast.  After you have cleaned the engine and treated the rust spots with RustBlast, then you will paint the marine engine with Motor Coater.

You can find complete directions for the Motor Coater Kit here: http://www.kbs-coatings.com/motor-coater-info.html