Since the overrun clutch is located after the tail/main rotor drive split, it is only subjected to the main rotor torque loads.
Really?
fly911's diagram.
Item 1 Shaft Inner Race and item 28 Adapter are connected. Item 28 drives the TR. The OR clutch is BEFORE the shaft inner race at item 11 and is subject to ALL the torque.
From the Shaft Inner Race forward to the main rotor is only subject to main rotor torque and aft is subject to TR torque. The torquemeter measures ~ TOTAL torque applied.
Explain in your scenario what would drive the TR in autorotation?
That skinny bit of Item 1 Shaft Inner Race leading to item 28 Adapter is what is driving the TR. It is probably about as thick as your little finger.