I had always thought that opposite rotation of props was achieved by changes to the propeller reduction gear rather than the engine itself?
Of course, the effect achieved would depend on whether the torque effect comes from the prop or the engine internals and I don't really know enough to determine whether one or the other is dominant.
It does seem silly to re-engineer the entire engine to rotate in the opposite direction necessitating two sets of spare parts if the same effect could be achieved in the reduction gear?