Led gas sign cabinet help needed.

I am currently bidding a gas price sign and I'm in need of some assistance. There is a 76 x 66 7/8 light box already mounted and I'm trying to figure out a way to mount 8 12" watch fire gas price signs 4 on each right side with the grades on the left. What are some ways i can mount the up there without having to put up a new box cabinet?

 

Yes remove the extruded sign face and replace it with the panels.
Yes i can fit them back to back. The only way i can think of modifying it would be to weld dividers in place to hole each insert. Each led sign weights 20 pounds. So thats a additional 160 pounds of weight. I would be more worried about the cabinet giving then the pole