I fabricated a fuel tank housing which sits nicely on the centet line of the engine and also accomodates the air retract cylinder. I have gone with Robart 188VRX and the 650 series 90 degree set. I have also fabricated new wheel doors which fit into the wheel wells . The engine I use is TT 91 Pro with a 3 blade prop 12.5x7 Graupner. The tank supplied by TT is rubbish , I went with a 18oz Dubro which sits right on the CG. It works well for me. Dont pay too much attention to TT's methods, the chaps on this forum have more ideas based on experience....