Nevenick,
As you know torsional stiffness is k=Torque/Thetha
and first find out the thetha in .f06 file by looking against the axis where you applied moment
(means if you apply moment at z axis, you will get thetha in R3)it will be in radians
and once you get that and you already know torque you applied,
You can easily get, what you want
Cheers
Abi