There arew a combination of bolts and studs, you might have missed some, plus it should be sealed with silicone goo tot he back of the box. You can split them in situ if you drop the gearbox a bit to clear the floor.
Don't know why it has to be in low box difflock unless that's to get the linkage int he right place when you reinstall. Of course those linkages need taking off as the lever sits on the gearbox.