A short levered shifter does not really shorten the linkage action. Hold your arm straight out and move it from left to right. The travel back and forth at your hand (original length) is a bit further than at your elbow (shorter lever). This is what cutting the lever does.
Rodney's kit acts to affect the 'real' shift linkage and is superior to a cut lever in all functions.
When doing a cut 84 shifter, here are two methods:
You can cut the top off your shifter and use a set screw to hold the knob. This keeps the kink in the shifter which brings it a bit closer to the driver.
Or you can grind the shift lever off the base, cut it at the bend and reweld it to the base. This gives a short, straight shifter which keeps the threaded top to secure the knob.
Some find that shift effort is increased, but I have both styles and would not use a stock length lever again. Besides, it's a freebie.
