I don't see how a header tank or a bladder tank such as the Tetra will push fuel to the engine.  It may work without this, but it's getting close.  Muffler pressure is good for 8  inch's of fuel head and the tank is 6" below and 2 to 3 inchs deep.  You may run out.  Also with little additional head it is going to have a larger reliance on suction, this means it will lean out more.  Because it is well below the engine a uniflow setup will not help, nor will a header tank, nor a bladder.  The only option for consistant running is a pump, or crankcase pressure with a regulator. </p>