What if you used the two engines to drive two generators instead of a psru? There is no propeller load on the crankshafts not designed for propeller load. The two generators each drive two electric motor driven propellers (4 electric motor driven propellers total). The electric motor driven propellers are symmetrically driven that is, one generator drives an electric motor driven propeller on each the starboard side and the port side, one generator drives two tractor propellers and one generator drives two pusher propellers or other symmetrical scheme. That way the loss of either generator still equals symmetrical power and thrust and you are just out the drag losses. A bank of battery's could supply supplemental and emergency power to the motors.