You'll want to find a VERY small LCD to put in there, and you should probably remove its casing to make as much room as possible. You'll want a Mini-ATX motherboard, and you'll need to cut some space for the I/O cluster. For expansion ports, you could make a rack of them from an existing case and fit it in there somehow. You might just want to go with putting your PSU outside the case, but if you have room, make sure it can ventilate properly. Also, passive cooling is your friend in this situation.