Since you don't care about the back plane, then all you need to do is tap and mount standard stand offs. Or rivet or push or weld. You simply make your own mount points. Any enclosure will work at that point. Assuming your board has mount holes.

Since you don't care about the back plane, then all you need to do is tap and mount standard metal screw stand offs. Or rivet stand offs or nylon push stand offs or weld. You simply make your own mount points. Any enclosure will work at that point. Assuming your board has mount holes.

Otherwise, some boards, depending on size, weight, and vibration, you can mount it with foam tape/squares.