http://www.burtonpower.com/ford-elec...or-revfss.html
http://www.burtonpower.com/revotec-e...x-revt9-a.html

This one? looks interesting. Let us know how you get on. I've mounted a sensor to the front hub which picks up on the back of the wheel studs which works fine. But that's a much neater solution if it works.