Just go on Amazon on search for 54w LED light bar. They're all basically the same light regardless of the name. They will fit (I used the ones by Rolinger). They mount from the bottom and are about as wide a light as you can fit in there. The limiting factor is the bumper bracket behind that opening. Take that cover off and look inside and you'll see what I mean. That bracket wraps around to form a box of sorts.
I also tried a 7" light with side mounts. I could have made it work, but it looked funny in the bigger opening. It also had more depth to the housing which caused it to stick out a bit from the face of the bumper, which again looked funny. I probably could have trimmed the rear cooling fins a bit to make it flush...
Look at the photo above, those lights protrude out the opening. Mine are recessed. If I wanted them to stick out I could have fit the 11" light that I tried, but it looks weird to me...