JohnM John I had the same problem with my 452 FE motor. Get a 1" piece of aluminium and make it your self Use the gaskets as a pattern. scribe it in the aluminium and drill and follow the lines, take the shape edges off, get 2 gaskets from pep boys for acouple of bucks and you have it. Buy a hole saw kit at home depot for a nice center hole. 1/2" might be width enough. All you need is a drill press. You can do it.
Rick Lake