Re: 60 Degree DIY Mid Hi
Yes, I see the differences in getting the XT1464 to fit ......and what that implies for the front grill.
Since the XT1464 is 380mm wide, and the exact same width as the PM90 (my name for your 90 degree box 
), it would take a 34mm increase in width (2 x17) to get the horn to fit fully in between the sides wouldn't it?
Which i think adds 3.4 lbs. (By my calcs, each 1mm increase in width adds close to 1/10th a lb in weight.)
Given the box already needs to deepen at least 25mm (I get about 1/12 lb per mm depth increase), the whole XT1464 thing seems to add about 5.5 lbs. (not counting maybe some saving from 30 degree back corner?)
So, my thought it to say to heck with fitting the horn fully inside the sides. I'm thinking to increase width by 8-10mm and recess the edge of the horn in the side walls, with just enough side wall to be sturdy.
This would mean no grill for XT1460 itself, and separate grills above and below for the 12" mouths.
Works for me...
As I like your original goal of super speaker on a stick... trying to keep it as small and light as possible.
Having said that though, if the goal is to put 2 or more boxes together, they are a lot less likely to be on any kind of stick, huh?
Anyway, I figure a box deep enough to accommodate the XT1460 would pretty easily allow interchange with the HF950.
I see the the XT is 304mm high, and the 950 is 300mm (when looking at front of speaker)
So the horn baffle plate for either could have same height. The trickiest part might be getting the 950 horn plate to dovetail cleanly with the recessed sides cut for the XT.
