Another answer to my question from Pelican Parts:
http://forums.pelicanparts.com/showt...dometer+pickup
It appears that the sensor "looks" through the case and "sees" a rotating magnet.
Most likely a simple reed switch, and the speedo counts the number of switch closures, but I am guessing here. The sensor is available from Pelican Parts in the States for 130.00, so if I am right it is an expensive reed switch but I need it. The more I think about I may give it a try with a reed switch, as by the time it lands here it will be 200.00 USD
The Pelican technical forum is a wealth of info on P cars, and where I found the box code info. There is also an interesting discussion of Swepco gear lube which answers my other question, but since it is non-available here I will use a GL-5 rated synthetic.
Now I just need the lever arm to connect to the slave cylinder