Easiest work around is have a RJ45 passthough for the MC Cthulhu and USB for the Brook UFB
If you use the 20 pin header correctly, ground and power will be shared between the two boards making it a proper dual-mod.
USB for the MC Cthulhu would be limited as most of the systems the MC Cthulhu supports will need more than 4 pins.
You would want the 8 pins afforded by the RJ45 as all the older consoles use up to 8 pins. (Some consoles have a 9 pin connector but only 8 pins are ever used).
I know there been Tech Talk regulars that built their own “Imps” from available off the shelf parts.
I just don’t have the semantic.