Ok for those of you who want to know, here are some pics showing how the external and internal gear/shifter locks work/mount.
First the external one:
It uses a mounting bracket that's cut out of really thick steel. The lock has a slot in it and it slides over the top of this plate. It then locks in position with two screws. The screws are easy to remove, but when the shifter is locked in place the shifter and u-pin totally obstruct any access to these screws.
Here you can see the screws that hold the lock in place on the mounting bracket.
Here's a pic of the bracket with the lock removed:
and a pic of the bracket again.
It bends at the bottom and then mounts on the floor of the car with one way bolts. Often the bolts are installed from the bottom, and the exhaust then obstructs any access to them. The plate could also be welded to the car, but that's too permanent for me. This steel is thick. I tried bending it forward to adjust it for my new short shifter, but it won't budge. Going to have to take it to the shop for a new custom bracket.
And here is the second type. Internal gear/shifter lock. These are much neater, and come as std on quite a few cars sold here now. The only down side is you need to cut a hole in your console.
The pics are of the lock on my s13:
Lock in use - very tidy:
Unlocking the lock:
The pin. Here you can see how I had to grind it down (again to adjust it after installing a short throw shifter). Had to grind for quite some time, just to remove that bit of metal that you can see there!
Here's how it locks the shifter in place:
Lock pin installation bracket:
And here is the pin when not in use: