The MPP1426, MPP1428, MPP1904, MPP1906, MPP1908, MPP2706, and MPP2708 have some additional tapped holes included in the stator housing.
The 2 holes on the top surface are typically used for eyelets to facilitate moving these larger motors around during the manufacturing and shipping processes.
The holes on the bottom surface are intended for additional mounting locations to assist in securing these larger motors in the installation.
However, these tapped holes may be used for additional purposes like securing cabling or other devices as long as they do not negatively impact the motor's thermal ratings.
Here are the dimensions/locations of these holes.
MPP1426 (bottom tapped holes only - no top holes)
MPP1904 bottom (hole dimensions same as top drawing)
MPP1906 bottom (hole dimensions same as top drawing)
MPP1908 bottom (hole dimensions same as top drawing)
MPP2706 & MPP2708 bottom (hole dimensions same as top drawing)
(note - L3 dimension = 8.70" for 2706 and 9.70" for 2708)
MPP2706 & MPP2708 top
(note - L2 dimension = 13.15" for 2706 and 15.15" for 2708)