Are Valve Covers interchangeable for side to side?

[pauls]

Want to add a breather on each valve cover. I can use the oil filler on one side, but don't want to hack up the other cover with a hole. Can you use a spare with s filler hole on the wrong side by flipping it upside down.

 

[WESTCOAST JASON]

They are interchangeable right side up, but you would want to plug the vent on the valve cover. I am pretty sure they wont fit 'upside down'