I was just getting to the end of all the new wiring when the same nice man in the same white van turned up with another parcel from RS containing the relays. Apart from a slight problem mentioned elsewhere I now have the 4 new proximity sensors wired up with screened cables back to the controller and the relay/transistor interface into the BOB finished and tested.
Tomorrow I will tidy up the impressive mess and get everything put back together and ready for testing and alignment. Auto-squaring will need to be re-calibrated and the finished aluminium (rather than the old plywood prototype) Z axis lined up as well. Might be able to make something soon!