Not a MC250, but I did rack mount a MC50, using a 3U shelf:
http://www.amazon.com/gp/product/B005GP ... acleint-20
Unfortunately, I don't have any pictures of the finished mount on this computer, but I could take some if anyone was interested. To get the MC50 to fit in a 3U space, it was necessary to remove its feet. I replaced the sheet metal screws in the base with Nut Serts
(for strength), and bolted it directly to the shelf. I also added a piece of 3/16" aluminum to the underside of the shelf as a stiffening plate. All things considered, I think it's mounted pretty solidly. It now shares a 4U Gator case with my CTP.
Dimensionally, the MC250 is about 1-5/8" taller than the MC50 and almost twice as heavy:
MC 50: Size 5-1/2"H, 8"W and 12-1/2"D. Weight 20 lb.
MC 250: Size 7-1/16"H, 10-5/8"W and 15-5/8"D. Weight 35 lb.
So yeah, as JonnyBoy said, you could do it but you'd probably need a 4U space or rolling cabinet to pull this off, and it will be pretty heavy when it's all said and done.