And don't pull it apart until you lock it in 1st gear!
Ok, so it can be done successfully without doing that, but it helps a lot. If you do that, you don't have to keep all your attention on not pulling the output shaft out so far that the inner roller bearings fall into the case.
There's a tool that you can make, that spans the two shift lever arms to keep one in neutral while the other is in first.
Well worth figuring out before you start yanking.
Paul