If that is the fuel tank, that is interesting. I thought about putting it there at times...it would eliminate the fuel pump. In the event of an off airport landing(crash), if the mast got broken off, would that be a bad place to have the fuel tank....above the engine, and right behind the pilots head? Possibly spilling fuel all over the engine and pilot? I am flying a stock style Bensen type...would there be any aerodynamic/cg effects with the fuel tank on the mast? If these things are not a problem, this might be worth looking into.