You can replicate this quite easily. Friend had a few adaptors laser cut a few years back which bolted onto the rear driveshaft with the same pattern as a electric speedo diff. You then ran a standard bmw speed sensor to it and voiladoes that M88 engine needs a "speed" signal to his ECU as it gets it from the diff in a oem M5 ? which of course you don't have in a E9 diff.