another electric fan ?

I agree with dodgestang. I have a 16" Spal on a slightly modified 289 in a 65 coupe with a stock three core radiator. The Spal is a nice package and fits with about 3/4 of an inch space between it and the water pump shaft with the Spal centered on the radiator. The relay is compact (I placed it under the battery tray) and sensor fits into the stock water temp sensor fitting on the intake-use teflon tape. I moved the stock temp sensor to the 90 degree elbow fitting for the heater hose. I drilled and tapped the top of the 90 degree elbow and used RTV sealer on the threads, no leaks!

A word of caution for any additional elec load like a fan might require a bigger alt. I eventually went with a one wire alt. The Mustang's original stock elec system is generaly not up to the task of modern demands. Good Luck
Steve