We had an IMac in the shop a month or two ago. It was really great; at some point in time it ended up being upside down on the workbench and it looked like some small four-legged, cycloptic animal had died on the bench. I had to fight the urge to get the masking tape and put a big "X" over the monitor. Regardless, you probably could find a few scrapped shells and use them to mess around with placement and such. I mean, you basically need to find a mobo that has what you need on it that will fit the dimensions given. It probably won't be much of a PC but it could work.
Things are more like they are now than they ever were before.