Sorry Funola, I have been remiss in not checking the replies over time...

I did build a custom analog controller for this purpose, but later went with an Arduino controller in order to make it simpler and easier for others to reproduce. I will post the sketch if there is interest.
These Volvo fans are cheap enough ($27) at the local U-Pull that I did not have them checked by hooking them up. They seem to be very robust, but I bought a spare anyway.

Update: I have had no issues at all with the fan & controller. The arduino has a lcd screen that I use to monitor the return coolant temp from the radiator to the engine block, which tends to remain very low compared to the dash temp. The dash temperature seems to be rock steady under all but the most grueling hot days climbing mountains at 75 mph at 6000' msl. Even then it only blips up on the gauge to about 100C, but even then it is more likely that the exhaust backpressure from the gt2256v working to make boost is the cause. I am not 100% sure if the electric fan & thick core radiator are the cause, but my fuel efficiency is also improved. Even when the electric fan runs at full speed and pulls 21 amps, that is still only about 300 watts... or .4 hp - that's less than 1/2 horsepower! I have made many trips up to northern New Mexico getting better than 40 mpg. I know there are doubters out there, so I have been very careful to fill the tank on the level, and use gps data to derive the miles.

Interesting factoid: Although I used a vacuum device to fill the radiator & cooling system a few years ago, it still took about 15 months for the last air bubble to work its way out. When it did, there was a significant improvement in steadiness of the dash temp gauge, the engine ran cooler under all conditions, and I had to add about 12 oz of coolant fluid. I am never opening the coolant system again... I can be patient - just not for air bubbles!