Hi Glen, here is a pic of both Diff and Gearbox
oil temp senders.
I use the engine
oil temp gauge only and 2 momentary buttons to switch between the senders. i.e. normally sits on engine
oil temp, press the button and it flicks to diff, let it go and it flicks back to engine.
The diff plug is 16mm, and I use an Aeroflow adapter NPT to Metric AF912-M16-02 for a 1/8npt temp sensor.
and i think from memory the gearbox is 18mm version also from Aeroflow.
Diff
Gearbox
cheers
Dave