I used Dupli - color engine enamel primer with ceramic and dupli-color engine enamel with ceramic color is: cast coat aluminum, bought them ay oriley's auto parts . You won't need a clear coat . I got all of the grease off with easy off oven cleaner and followed up with acetone. No fish eye when I spray the paint. There are a lot of imperfections in the casting but that would take too long to sand out. By the time you put back on the coil packs and engine cover you'll never notice it.
Where did you get the aluminum screws ?