It's not a silly question, but you won't like the answer: there isn't one.
The Crewe-specific precursor to what we now know as OBD-II was introduced on the 1992 model year and was known as Mastercheck. It used a diagnostic box and connectors utterly unlike anything that is used for what is now the industry standard.
See the attached image for the workshop manual page that shows the Mastercheck diagnostic equipment for the 1992 model year forward. I would have to imagine that Crewe transitioned to OBD-I and, later, to OBD-II/CAN, but I cannot confirm that.