There is a lot of chatter on the internet suggesting how to solve your problem. The idea of putting in radiator drain was what some mentioned. NOT acceptable. Must be on the engine. As you are talking to the radiator people and the Fan people, it would seem that one of them would have given you the best place, in your case ,to put the switch, which is what they call the fan temp sensor. As you may know, A pull fan mount is best. If you use a push mount you can install it outside of the A/C condenser in front of Rad (which cools the condenser for better performance of A/C) and keep the mechanical fan. This is also a good option. A "switch" can be installed in the liquid line of the A/C to turn on the fan when A/C is on. or fan can come on with ignition switch or a temp switch as you are speaking of. The idea is to co ordinate what the coolant temp sensor is sensing with what the fan switch temp sensor is sensing. If they are sensing at different/wrong/cooler or hotter places, the fan will not be coming on and turning off at the correct time relative to engine temp. It will be operating by what it sees as correct turn on turn off temps but that may not be what the engine needs. It "boils" down, in my opinion, that if you can fit the switch into a thermostat neck, that is your best bet. That's if you don't want to drill and tap the intake. Could you put the heater on neck and sensor in manifold? Remember crazy ideas lead to good ideas soooo...Use the manifold port for fan in summer and for heater in winter. (don't like "T's") Two other points: I don't know if you have open or closed system but I do not believe that engine should be getting hot. You have got a problem with thermostat range , radiator cap pressure or a water flow problem or shroud design and location. That radiator should cool it 'no sweat" without A/C. You should fix that before moving on. YOU DO have something screwed up. Point 2. You may find that a controller is necessary to obtain the best result.
Shrouds should cover entire rad, fan blades about half way into it maximum with about 3/4" minimum stick in. The shroud is very important. Your 3/4 distance from fan blades to rad is too close to get the proper flow and for a shroud to "gather" air from the edges of rad. Also the shroud should be fairly tight to O.D. of fan. At less than 3/4, there is no shroud geometry that would obtain full flow. Move rad forward, mount electric outside of condenser, keep mechanical fan, find shroud that meets the design requirements.
