I used to own an 85 Nissan Maxima with the V6 3000 engine and it had electric fans (2 fans). I wonder if these fans would come close to fitting the radiator. It wouldnt hurt to measure your Z's radiator and head down to a junkyard to see if it would fit. Good luck
With my 2 stock electric thermostat fans one side is on all the time, and the second side kicks in when it's warm. Plus 2 fans fit nicer than one huge one... Not exactly sure why Nissan decided to have 2 electric fans for the Jap/Aus models and not the U.S model but I'd say it was done for good reason.
On the AU NA, neither fan should run all the time unless you run the aircon all the time.
Without the aircon engaged, the RH fan runs at about 2/3rd speed when the 100°C switch in the LH side of the intake manifold closes.
Both fans run at full speed when the 100°C switch in the bottom left of the radiator closes.
When the fan/s are on, the ECU gets a load signal which prompts the ECU to bump up the idle speed via the idle-up solenoid (or via the FICD if the aircon is on).
The staged operation minimises the electrical load and bumping the idle helps with that as well. However, most people converting to twin factory e-fans might be daunted at the prospect of wiring 3 relays and two temp switches and maybe a diode.