This morning I picked up some Dec stuff :
Great haul!
...which forks into 4 D25 connectors.
This sounds like a possible updating of the QBus board
CXY08 / M3119 and the cable BC19N which is in fact a
4x2 line Asynchronous Multiplexor. If you see model
numbers like these printed on anything that would help to
confirm it. FYI
John A.