Hi Tomcat
It seems like a fairly simple operation- I watched a Youtube video some months ago.
Basically you would need to get a new sump plug with a sensor fitted to it. I'm sure that they're available on Ebay or Amazon, but you'd have to check that you get the correct thread.
The back of the gauge has 4 connections; One obviously goes to the sump sender unit. Then there is an earth connection and another goes to an ignition terminal so that when you turn on your key, the gauge becomes active. The 4th connection is for the gauge lighting, not too sure where you would connect that.
that being said, I believe that engine oil starts to deteriorate at 130 degrees C. At that sort of temperature, the water in your car would be boiling over already so personally I would rather have a water temperature gauge and perhaps an oil pressure gauge.
I'm sure that I have a little oil can symbol on my instrument panel, but I'm not entirely sure what it's function is, pressure or temperature