Hi Alex,
I'm currently sourcing the parts to do this, it's not as easy job to get the full system working.
I initially swapped the control panel without any sensors and this did not work properly, the air vents started to act strange, this is because the loom for the evaporator box was still the non the thermotronic (851) version.
To get the full thermotronic system you need the various internal and external sensors (inc new head control unit), 851 evaporator box, rest rump, center console and also rear vents. You can get it to work without the left/right position and rest functionality with just the sensors.