I would not go 30% flat! Just use Eastwood underhood black. It's easy, sprays nicely and looks great. I have my pulleys, fan and brackets powder coated semi gloss. It looks fine if it's a little glossy but not too good if it's too flat. You don't want your radiator too flat either. I would stay away from trying to do a certain percent flattener. It's tricky and there are plenty of good paints out there of varying glosses.