The first machines manufactured by PCS were PDP11 clones. And in order to improve these clones PCS developped a CPU-board that was using a Motorola 680×0 processor instead of the LSI11. But the remaining parts were kept. In particular the bus in a cadmus box is a 9-slot QBUS. And most I/O-cards are identical to those used in PDP11’s.
Seems like a Cadmus 9200 is a PDP11/23 clone with 680×0-processor and modified memory-boards.
Accorindg to cadmus-documentaion the serial I/O-board in a Cadmus is a DLV11-J (DEC part number M8043). Most likely I can replace the missing serial boards with such a DEC board.