Cleaning up engine bay for paint questions

Are you using an HVLP gun or rattle canning it? Assuming HVLP I would prep and paint the engine bay just like the rest of the car. Typically that involves an epoxy primer / sealer over the existing metal/paint and perhaps a single stage urethane paint. You have to ask KBS what is required to paint over top of it. Perhaps top coating is covered in their instructions.