Can't find a JD A587 R head for a 1937 Model A anywhere. Can anyone tell me if a HA 587 Heisler head will work on a standard JD block with standard pistons? Will the rocker arms and push rods work without any modifications? What kind of other modifications, if any, will have to be made for this head to work? I have a new head gasket for a A587R head. Will it work on the HA 587?