I ran an MSD Atomic with my engine. Put your gauge water temp sensor in the water pump and the MSD Atomic water sensor in the regular block location. The Pantera water temp gauge is not exactly accurate, unless you get Jon Hass's calibrated sensor. That way the Atomic will know the coolant temp correctly at all times. I would not worry about the Atomic controlling your cooling fans. If the Atomic water sensor failed I doubt the engine would run anyway and you could control both fans with more accuracy. A better solution would be Jon Hass's fan controller. His unit uses modern sensors in the radiator with a low speed - low current start of the fans and proportionally changes the fans speed depending on temperature minimizing current draw and noise.
When fitting the Atomic throttle body consider spinning it around so the throttle lever is on the right. The fuel lines then take an easier line to the left side. You might need to lengthen your throttle cable though.
You will need a tach adapter if you are using the MSD ignition box and want to run your original tach. I would use Jon Hass's tach adapter, my MSD adapter was not accurate and eventually failed. Better yet uses Jon's ignition box and a lot of your worries are solved.