The Murray aluminum radiator has a plug there. It's the middle one of the five things on the bottom in this photo: From left: radiator hose fitting, drain port, port for temperature sender, then the ATF ports. This sender - I believe - is for the PTC heater under the carburetor - if you have that, have it working, or live in a quite-cold climate. So you likely don't need that.
There's also a temperature sender on the engine for the emissions system, and of course the temperature sender near the thermostat outlet for the temperature gauge in the dashboard.