I had the same problem and had to remove that little section on the bottom part of the headbox that the BG slots into. I then chiselled it out to a depth of about 5mm
If I had routed out the top part the windows would not have matched up to the displays.
One display did not match up perfectly, so I moved it slightly ( drilled new holes ).
I dont really like doing a dodgey like that but sometimes you have to in order to allow for manufacturing flaws!
