It would appear that a logic board from a beige G3 or AIO will fit in an LCD-equipped CC, located almost vertically across the width of the CC, located far enough back to leave room for the floppy drive, with the top angled towards the front of the CC where the case top is higher.
Obviously, this awaits the LCD in CC project.
Obviously, looking at eBay it will be cheaper to buy a complete beige G3 and use all the parts than buy all the bits separately - that's why people are parting out beige G3s now.
Since the board can take G4s at 400Mhz (or more?) it could be a pretty impressive CC, and beige G3s are getting cheaper by the day. :-)
Forget all the complexity of iMac and Cube boards. . .