2 pcs of M3x8 screws are used to mount the holder onto the LGX to the top threads on the sides. 

4 pcs of M2.5x4 screws are used to put the sensor board onto the holder. I recomend cutting the M2.5 threads into the plastic before mounting it. Depending on the plastic and/or printer precision the screws might be able to make the threads themselves. Also two of them can be much longer to hold the sensor more securely. 

There are cavities for the protruding part of the pin headers. If the soldering is half decent it should fit comfortably to mount the board flat to the holder. 

If the board is mounted with VIN pin bottom left when looked at from the front of the printer then the config line for RRF should have M955 Pnn I50 in it to tell the axis orientation.