If you have a properly working stock exhaust manifold, there is no need to modify the valve. If you have a Clifford intake, hook up the water jacket. If you are using headers or Dutra Duals and a stock or Offenhauser intake on your slant six engine, you might want to try this heater upgrade for your engine.
For those of you with a 240/300 Ford 6-cylinder engine, we've got an intake manifold heater kit for you too. A design feature of this Ford part is a flow diverter wall that directs water flow to the heater recess in the intake manifold.