Not sure I'm understanding the left handed box thing?
Ahhh...right...when you open the box, the foam inside has all the slots pointing to the left...so the fly goes in with the eye to the left, bend to the right. Every other box I have (Mostly Wychwood Viewfinders and C&F) the flies sit the other way round.
If I remove the fly with my left hand and thread the leader with my right, I have to turn the fly around.
So, my conclusion is, its a left handed box