To even more specific you want an adjustable Ambient Temperature Sensing Relay Circuit for this application. Since you want to move heat out of the engine bay you want to to use the engine bay's ambient temperature to do so. I am adding one and maybe two for the same purpose. It should be adjustable so that you have options when locating the temperature sensor. A secondary option would be to have them operate with the radiator fans. It would work, but definitely not optimally since the radiator is up front and responding to coolant temperature and AC activation.
The Fan.... I'm not a fan expert but I have noticed that the fans, I am using, exert more cfm when the air flow is pushed through the open side. I have no way to measure the delta, but I would estimate it to be 30% less in the other direction. Your fans may not have this characteristic, but it would be a good idea check this prior to install or to leave the option of reversing the fans mounted position.
Just my $.02. HTHs