Thats pretty tight, Not sure how big the cube MB is but I think that would be the only one that small, other than the mini. Brand new Mini may be cheaper than using the cube board anyway, depends on how many parts you have already.
PB G4 15" 1.2ghz - Pismo G3 400 mhz - iBook G3 500 "Jukebox"
"SawSmurf" G4 500 - Quicksilver G4 Dual 1ghz modding...