I thought I'd update this a bit further.
Having looked at the gauge wiring, it turns out that all the wires for MFA are already fitted. This includes the violet coloured wire for the MPG input. However, this wire only goes as far as an independent connector. Meaning I will have to extend the wire to the ECU (hoping the ECU will have an MPG output programmed in).
I still need to wire in the stalk, this will be done once the parts arrive.
Looking in the engine bay, close to the oil filter housing, there is an unused green wire with a spade connector. I'm hoping this is for the oil temperature sensor.
I still need to look into the wiring for the air temperature sensor. I think I will end up having to extend some wires from the fuse box for this.