I have one of these on a No.1 Mk.1. It appears to have a movable level on the left side of the receiver which can be moved rearwards, to allow the base of the sight to pivot from the right side, yet NOT enough to allow the bolt to be removed for propoer cleaning.

Does anyone have any Exp with these at all? I am sure I am missing something but don't want to take a screwdriver to it to dissassemble before I ask the old and the wise here.