Get it cleaned up then a coat of auto body Gray primer surfacer. Then I have been using 2003 Dodge Caravan Silver Metalic in the Basecoat Omni line by PPG. Then Clearcoat over the silver basecoat with a good quality automotive clearcoat. 2 coats, will stand up to oil and gas.
And side shots of painted cast iron intakes. Basecoat / Clearcoat paint