It would be a lot of work and expense to install a sensor and gauge. I installed a AZIJYV OBD2 Head Up Display. A lot cheaper.
I put it on the left end of the dash for the shortest run down to the OBD2 port, tucking the cable under the door seal. What you see below is the temperature after the car was started and ran for a bit and is now cooling down.

Set the Alarm to 234° F for these cars. Normal Operating Range is 100° C – 108° C (212° F – 226° F). When you see it cross the 100° C (212° F) mark, the factory thermostat is mechanically programmed to start opening at 105° C (221° F) during normal part-load driving.