The bearing blocks are interchangeable.  Therefore, each block can be used with either the right or left motor-axle assembly.. 

• Carefully align and insert the motor and axle assembly into the bearing block as shown:

The bearing should slide smoothly (yet tightly) into the bearing pocket on the block.

The bearing will completely seat itself after you have installed and tightened the (3) socket head screws and standoffs in Step 5.

Note that the motors are mounted at an angle to the bearing blocks as shown above.  This is by design, and results in a larger usable surface area on the Arlo deck, by minimizing the cutouts (for the motors) on Arlo’s main platform.  There is only one orientation of the motor with the bearing block that will allow the three particular holes to line up for the bolt and standoff assemblies.   This orientation is shown in the above photo which depicts the left drive unit.