J Daddy,
The Little Showcase Factory website does show O gauge wall cases. Open up their "Store" on their homepage and go to the second page. They have two different sizes listed for O gauge. The cases (8 cases in poplar) that I have are 56"L x 27"H x 4"D, which they no longer show. Rather they now have 68"L X 33"H and 44"L X 27"H. Also, the doors are not glass, but are a clear acrylic. I got the cases to keep my modern engines fairly dust free, with all of their electronics. I don't worry about the prewar and postwar engines. They relatively easy to maintain.
Installation is very simple. They are pre-holed for mounting and brass screws are included. I would guess that with measuring many times and checking the level many times, it probably took me 15-30 minutes/case.
I am very pleased with the cases, and if you are ordering several, be patient. But, it is worth the wait.
George