Two last must do's :
1. First mount the door handle, and the last job to do is to push in the lock barrel, working from the inside of the door. Is a bit fiddly, and the rod can play tricks on you to get in the wrong angle. So before mounting the handle in the door, through the hole pre-position the barrel so it is in the right position. Next mount the door handle, fix the screws, and finally pusth in the barrel. Doing it in a different manner makes fixing the screws much more difficult. 
2. The u shaped spring that holds the barrel must of course be mounted in the door handle before mounting the handle, so the barrel can snap in. But from the factory this spring is positioned with the legs downward, so the top of the spring is in a position that makes it very difficult to remove for dis-assembly whenever needed. You can hardly pull the sping out. So better is to turn the sping around 180 degrees, so the legs are pointing upward. This way the U shape is facing downward, and is easy to remove from the inside of the door, whenever de barrel needs to be removed. 
I also know why MG engineers thought the tedious way was better : in my way the end of one of the legs is in the way of the mounting screws, so the mod is to cut a little bit from the end of one of the legs so it is no obstruction to the mounting screws. Not too much, just a few mm. See the pics for understanding if this last instruction. THe red arrow shows the spring to be turned around. The red line shows where to cut a few mm off the spring.