Re the question about the free-running turboprop not directly connected to the propeller--
Torque is torque. When the prop speed is constant rather than changing, the ultimate reason the engine needs to exert torque, is to overcome the drag of the prop. It doesn't matter how the different bits are connected. If prop drag somehow vanished, the engine wouldn't need to make any more torque (except I guess to overcome mechanical friction-- but that torque is all "recovered" by the friction and no net torque is imparted to the airframe). Also if prop drag somehow vanished, the slipstream would no longer be spiraling, it would just go straight back. Prop drag causes the spiral. It's all connected.
I liked the way the author brought it around to an issue of conservation of momentum here
*9**Roll-Wise Torque Budget :
"Using Newton’s law again, we see that if any air escapes while still rotating down to the right, the airplane will roll to the left."