Back in the day, Shreve Systems sold an "upgrade" to the IIci in which they would replace the IIci logic board with a Q650 logic board. The Q650 and Q800 logic boards are the same, with only tiny differences in installed components.

IIRC, the rear port openings must be modified to accommodate the different arrangement of the Quadra ports.

I think, but am not certain, that a Q800 board would fit into a Q700 case without modifying either the case or the rear port openings.