1962 235/261 engine?

Where does the probe/sender enter the block? Near the top of the head?
Does the sender/probe diameter match the hole in the head?

If yes, drain a quart of coolant (save it).
Remove the old probe.
Screw in the new probe.
Pour in the coolant.
Put the radiator cap back on.
Start the engine and check around the probe/sender for leaks.

If I am incorrect, this will be corrected.