Actually, as I was about to build something, I traded an old SM58
straight up for a steel rackmount on casters. You know, one of those half-upright, half-tilted deals. Anyway, I found that if I reserved the lowest 3 rack spaces on the slanted part and placed a deep rackmount unit in the top space of the straight part, that the API 500-6B
sit perfectly in the reserved 3U with it's back feet resting against the lower straight-mount unit and its front feet resting against the bottom edge of the rack.
I'm not around my usual computer, so, unfortunately, I can't upload a photo.
The only drawback to this placement, thus far, has been the fact the I have to pull the Lunchbox out of its place if I need to rewire anything because there's no room to access from the rear. However, I do this very rarely as I have it normalled with the rest of my equipment via patchbay.