As mentioned earlier, one of the tell tale sign of a 7sz is the larger rewind knob but some regular 7s had this as well. Another more subtle key difference is the position of the vertical RF adjustment screw. On the 7sz it is over the second “n” in “Canon 7s” on the top left (rather than top right next to the shutter speed dial) of the camera, since the improved mechanics on the 7sZ uses a cylindrical rotary prism between the RF mirror and the camera chassis.
The horizontal RF calibration is the same as the Canon P and is located on the front of the camera between the viewfinder and the frameline window. Good to know as the rangefinders are sensitive to knocks and it’s nice that you can adjust it without opening the camera up. Experts have said the rangefinder on them are even more complex than that of Leica Ms.