I did mine a few months back when I replaced the selector shaft seals.
As others have said, it will come out while the gearbox is still in the car. I got mine out from underneath and the job gets a lot easier if you slide the brake/clutch (?) pedal shaft out of the way.
Like MacVP says, pay attention to the position of the rear selector fork as it is on an offset with a front and back. It is possible to get the side plate back on with the rear fork back to front. Don't ask how I know this.
Also have a look at the distance between the rear selector (1st/rev) and the front radius rod. If your gearbox mounts are compressed/collapsed, the selector will foul on the radius rod and you will struggle to find 1st when you have a load of passengers in the car. You might want to replace the mounts while you are under there. They are same as the engine mounts and are easy to replace.