Peewee,
The kit model is KC5381 and cost under $30.00.
You can sense the temp using the thermistor anywhere you want.
I have mine tucked under the end of a radiator hose (outside the clamp) so it doesn't contact the cooling fluid. You could clamp it to the thermostat housing and adjust it to the temps you want.
Mine has run without any problem and I had the joy of building it myself.
When my new engine goes in I can change the settings on AND off to whatever I want. The switch is accurate to within 1degreeC of what you set it at.