the og cheesegrater has a LOT of room for (dual) CPU coolers, a space for 4 drive bays, and the height of a power supply shaped to fit behind the stacked height of multiple optical bays.
Once the opticals are gone, the power supply can be thinner, but use the whole footprint, like the 7,1's does.
Probably look at the 7,1, power suply at the bottom, plus the height of two full-MPX bays, then processor, ram and (on a separate card) default IO above that, possibly even on a 90 degree mounted sub-board, like the way the 4,1/5,1 cMP processor board is.