There is a very simple way to hold a mountain-drive against the reaction torque. The housing with integrated anti-twisting bracket doesn't need any modification of the frame at all. The clamp is connected to the rear chainstay. That's it! No chamfering, not even a high tightening torque is required.

You can even bend the lever some millimeters to adapt it to the chainstay perfectly.

One more big advantage is the use of adapter rings. These adapter rings allow to fit a mountain-drive into any diameter of bottom bracket shell (photo shows a mountain-drive with a pair of adapters for diameter 40mm).

The version with torque lever allows also the use of any type of chainguard holder, that is clamped between bottom bracket shell and bearing / gear housing.