Jim,
Motor is already pretty low, thankfully and the rotors are pretty high.
I think raising the gas tank is a fantastic idea.
As far as the rudder/tail goes, I would look into adding an HStab that goes between the rudders/VStab through the prop wash. It would be so long that even a thin one would have a good deal of surface area.
Since the thrustline offset is only a few inches high, I doubt you will need a super huge HStab. Also, keep in mind you do have HStab area already out in clean air.
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