The rectangular fork that the lever pivots within is a two-piece unit which only appeared in early 915 shift housings. The photo shows you have the standard shifter, not a factory SS kit. The factory short shift fork is one-piece and has a humped or curved top section and the pivot pin hole is offset toward the hump (see photo below).
OTOH, you might have an aftermarket SS kit made by Weltmeister or Target. Compare the length of the lever below the pivot pin hole the upper lever in Jim's post with yours. The aftermarket SS units include and need a spacer to maintain the correct spacing between the ball end and the shift tube. Note: This is because the shift tube height is fixed via its mounting on the chassis tunnel.
The OD of the WM shift lever necks down from approx. 19mm to 15mm at the shift knob end. The WM lever is also significantly shorter than the factory levers (above the pivot point).
Early 915 shift linkage on left (Sportomatic on right):
Factory Short Shift kit: The only interchangeable parts common to the regular factory shifter are the carrier plate (with Rev lockout pawl), the rubber buffer plate (at 10 o'clock) and the pivot pin:
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