Could it be the same as XR4x4 rear hub? If so it will be a 41mm socket.
Where abouts in Suffolk are you? I am putting a cossie lump in my 7 type kit car and really want to have a look at a engine that is running just to solve a few little questions in my head (like what goes where when it comes to cooling etc) If your anywhere near Stwomarket I would be more than happy to lend you my 41mm socket in return for a quick look over your engine!