351 C casting numbers
Casting #s I don't know but why would you need an aftermarket timing cover? I've never seen one. After all, it's just a flat piece of steel. However, if it is badly corroded, you might need to replace it. If you replace it, you could A: paint it. B: chrome it. or C: have it JET-HOT coated, Any of these will stop the corrosion.
Some people can break a cannon ball, in a sandbox, with their bare hands.