RE: position of jet engine in model...
I'd move it back a little more, so the longer inlets allow fuel between. Nose unit will counter the vertical fin weight and radio/valves etc the tail. Tail moment and nose length with cockpit etc will be fine. Ali is right fuel near the balance point is more important and any angle on the tube could mean big pitch changes with power on/off. Depends how you are rigging the wing/tail incidences
Dw