Sorry to say I can't really help
I have an original factory Rover SD1 workshop manual, the sensor is shown in the exploded view of the engine, just referred to as a 'transducer and pickup lead'. Under Ignition the manual states that the timing can be set via the engine diagnostic socket (showing a drawing of the sensor), and to connect the 'diagnostic equipment'. There is no detail of the diagnostic equipment, and there is no mention in the 'specialist equipment' section
In the workshop manual the catalog code for the special equipment begins with SMD, for example the cruise control fast check is a SMD 4050. It may be possible they made an ignition diagnostic in that series. I do also have some Lucas diagnostic tools for Rover, they begin with YWB, for example a YWB129 is an electronic choke analyzer. Maybe you can keep a check on ebay, or other auctions to see if anything appears
My understanding is that the diagnostic socket on the SD1 fell out of use as most garages would use a stroboscopic light, so maybe very few diagnostic devices were sold.
