WCA's Version
Get a bit of threaded steel. Drop it down the middle of the gear stick until it stops. Thread a bolt on to show where the top of the gear stick is.
20160326_140748 by
WCA!, on Flickr
This is how much the shaft has to lift to get over the notches. This is resting on the stop between Park and Reverse. Surprised how little rise is required.
20160326_140809 by
WCA!, on Flickr
And the news is in. The shaft has to be 11cm to reach the notches plus what ever you want to stick proud of the top of the gear stick. That is the bit that the gear knob will fix to.
20160326_140951 by
WCA!, on Flickr
To be continued when I have whittled a gear stick