You can also buy a replacement rubber cap that went into the valve covers of GM engines both inlines and V types in the early 70's. Made of black rubber and says OIL on it. Just pushes right into the breather and vent tube holes. Obviously it doesn't look as clean as using the earlier valve cover with only 2 holes on the top but will get you bye until you find the cover you are looking for. Any auto parts emporium should have them for about 2 dollars. Usually found in the aisle with PCV valves and oil fill caps.
