It is called a surface gap plug and is designed to run very cold The center electrode is completely encapsulated by the plug shell and threads and id kept cool by the head and water jacket.
They do tend to foul easily but If cleaned regularly, they can last the life of the engine. The plug is only "bad" if the center electrode is worn down below the surface of the porcelain insulator.
To answer your question: Good plugs to use would be Champion L20V, UL18v, NGK BUHX or BUHW or Mercury Champion L76V