Dan,
The rear sensor can be found once the prop is removed. It`s just behind the flange that connects the prop to the diff (so just one bolt to remove the flange)
.
I wonder if you could rig up the set up that a lot of kit cars use for the speedo sensor on the front hubs, do you think that would work Martin?
I know that TVR`s use this type of idea.
Regards,
Ian.