You'd be much better off putting your temperature sensor where the coolant enters the block. That way you are using the OUPUT of the radiator to control the fan. That is how it is on my 1 Plymouth when I converted it over.
It is also how the OEM's have done it for years. Which to clarify, is on the engine side of the T'stat not the radiator side. This will give you the most accurate reading of the engine temp.
Putting it anywhere else can be misleading/ disastrous if the thermostat malfunctions as you would then be reading the radiator coolant temp not the engine temp.
Spal sells 2 preset sensors that I have had very good luck with. They can be used with normal 5 pin relay (available anywhere).
they control the fans by grounding the relay coil. I have new ones still in the packaging, If anyone is interested PM me
TS-185 it turns on at 185 and of at 165, I have One
TS-195 it turns on at 195 and off at 175, I have 2 or 3
Pretty sure I even have a few or their wiring kits. if anyone is interested PM me
