If you know the transmission rating in shp, and the rotor RPM, then you can figure out the torque, but why?
I'd be interested in the power required to hover the helicopter, not the torque.
All the theory and non-dimensional analysis uses power (or some variant of it) but I've never seen torque used, except for presenting a power-required curve in terms that the pilot can use. That would be a good reason to use torque.
Unless there's another reason....