Use a copper gasket between the heads and manifolds. They are a bit pricey but readily available at parts stores and e-Bay. I always had leaks until a fellow Edsel club member told me about them. Even though I had the heads and manifolds machined, they eventually leaked. Using the later manifold with the donut gasket is a good move; seals much better and you will not have a leak down the road. Most FE manifolds (i.e. 332, 352, 360, 361, 390, 391, 401, 406, 427, 428) will work as long as they have two bolt holes on each port; one top and one bottom of the port. Some HP manifolds have four bolt holes at each port and will not fit your application due to steering box interference. The HP manifold is a sort of cast iron header that flows much better but because of this will only fit '60 and up chasses.
Good Edselling