Looking at the sensor pictured the 4wd must be a different cable end to the 2wd one, that has the inner sticking out about 1/2" or so, and a bell shape that sits in the speedo drive, a circlip goes on top of the bell part and secures in the inner groove of the drive part to hold together.
TVR I would have thought would have looked into this when they used the T5, but assume they had no luck ?, as they used a ring around the output flange on the diff and a sensor picked up off of this.
It's a very easy job to locate a sensor somewhere else, such as counting the prop bolts etc, then just calibrate, most can be done with a bit of simple maths or even a sat nav to hold at a set speed then "zero" the speedo gauge in that way, can also build in a little safety margin that way as well!!
tabetha