I'm sorry, I should have asked if you had a car or truck to put your motor in. The car engines were orange with silver valve cover, the truck motors were green. Again, the green is the same as the flathead V8 motors in 1953, so the green is available from your favorite flathead supplier. I am not sure about the valve cover on the trucks.
I am not sure, but '53 Mercury motor green looks a lot like '53 Ford truck engine green. Something to check in to.