From the fiducial report the Solenoid is 8.224065 inches in length on average which is 208.889 mm in length.  Distance to center from entrance end plate is 104.36 mm.  
104.450 mm from entrance end plate wil be defined as z=0.

Distance from entrance endplate to plane of cathode is 3.6135" = 91.783 mm

Measurements will use a right handed coordinate system.