I agree with the grease and wax remover. I've painted blocks in the past using brake clean, carb cleaner, lacquer thinner. It all evaporates to quickly. We always use single stage urethane. The only thing that seems to harm it is the dye from race gas can stain it. Everything else won't touch it. I'm not afraid to use bondo either, holds up perfect unless it's close to the exhaust, IE BB valve cover with stock manifolds. You'll notice my heads have no casting roughness or Indy logo. I have a bondoed factory cross ram that has the same finish as the engines in these pics that was bondoed and painted over 15 years ago.