We installed the Kartboy short-throw shifter and poly shifter bushings in the WRX this evening. The shifter itself was a snap to install: unscrew the shifter knob and pull it and the boot off, then unbolt the 12mm pivot bolt and nut, "pop" out the shifter pivot ball, use a mallet to hammer the new shifter pivot ball into place, swap the pivot sleeve and bushings over, bolt in the pivot bolt, and reattach the boot and shift knob. Viola, shortened shift throws, and a lower knob location.
The shifter bushing was cake to install too. Raise the car up, unbolt the
12mm nut holding the stock bushing in place, pry/coerce the old bushing out,
slide the two new polyurethane bushings into place on each side of the shift
rod, slide it back onto the bolt, and tighten the nut back down.
After a quick drive, I'm pretty happy with it; throws are shorter (but
because the new shifter relocated the pivot point, it doesn't require
additional effort, as a real "short shifter" ought to be) and
far more precise because the pillow-soft stock bushing is
nowhere to be found. Despite what I expected, I'm not noticing any
increased vibration in the shifter; I suspect that if we would have opted
for a solid metal bushing, it would be a different story. Overall, a
worthwhile modification: this is how the car should have been from the
factory, rather than the imprecise shift feel that it offered originally.