The mounts are considered as beams, seen in the side view.
Sections should be taken in a plane parallel to the ground.
Note: The minimum second moment and the minimum cross sectional area may not be in the same place.
Take the area and moment of inertia of the one mount.
If they are identical, these values can be multiplied by two.
If they are unique, add the values from the second mount.
If mounts are identical, R is the same centroid distance in each, and is the value used.
If mounts are asymmetric, average the centroid values for R.