The best way to do it is to remove the lead screw, remove the apron, and then remove the carriage. If you still want to remove the QC gearbox you can do it any time after removing the lead screw.
To remove the lead screw, place the appropriate socket on the first of the double nuts holding the lead screw inside the QC gearbox, then run an extension through the hole on the left side of the QC gearbox reaching through the hole to drive the socket. An air wrench will make quick work of removing the two nuts.
Move the carriage to the midpoint of the bed then remove the right side lead screw support. With the worm drive groove down, pull the lead screw out the right side of the lathe. Note that the worm drive key can and probably will fall out, but is easily reinstalled later.
The apron is quite heavy and will fall when the 4 (I think) cheese head (fillister) screws are removed from the front top of the carriage.
The carriage can be removed after taking off the rear bed gib.
If I remember correctly, the QC gearbox is held on by 2 cheese head screws that go through the top of the bed. It would be prudent to remove the banjo before removing the gearbox.