This is going to be the end of me.
Too much torsion and looking at it am not at all surprised. The classical way to build a fuselage is using stringers, longerons and a stressed skin and this is missing the latter.
Strength in compression however is remarkable and mainly thanks to that stay at waist-level that is slid into place like a pair of trousers... there's around twenty-seven kilos up top and barely a bend in eight millimetres of tie-rod.
There may yet be an argument to say that the torsion might not matter when it comes to flight. Anyone who's sat at the back of a 757 will have noticed the twisting along the length of the fuselage, or seen the belly of an overly-stretched DC-9 buckling under the load over bumps on the taxi-way.
Or indeed wings, which are able to flex in the case of the 747 over an arc of thirty-five feet.
Problem is, lacking the software the only way to find out is to get it airborne and that's a long way to go down what might be a dead-end.