Anyone able to tell me what this sensor on the back of the head of an AU VCT engine is for (picture to come tomorrow)? Looks to me like a temperature sensor - is it a relocated version instead of on the thermostat housing? Do most people use this one of the EF/EL one when doing conversion?

Temp sensor, you can run your wires back there to use that sensor instead of the E series thermostat housing sensor as it is compatible or just ignore it.
It measures head temp and not water temp so it provides a reading when you run out of coolant.

So it's a better option to go with then? I assume the plug connection is the same just have to cut and extend the wires? I'll run the AU thermostat housing then I guess. Actually I've still got to run the EF bottom part of the thermostat housing as I need the line out to the LPG converter which the AU bottom doesn't have.

plug connection different. can use either, the ECU will translate both senders to the cluster