I am very interested in having the layout as far as you have come to rebuild it.... In Italy the Ferguon Bigboard 1 was first cloned and then modified in the wiring diagram and firmware. The updates consisted of 4MHz clock, FDC 1797 and 256KB RAM. In the firmware were added in collaboration between ADE Elettronica and the Politecnico di Milano commands to manage the geometry of the disk drives. You can read the story in my web site also with English translation https://www.vintagesbc.it/vintage-computer-board/collezione/ferguson-big-board-i/ Obviously I have the firmware and the wiring diagrams of the modifications if you are interested.