If you are going to drive the car around town, the stock cooling system is fine as long as the radiator core is clean and free of oil and other stuff that gets blown in by the fan (like bits of old belts!), and all the cooling tin is installed and in place. Both belts need to be properly adjusted and in good condition so they do not slip, and the fan shroud needs to be in good shape. The fan needs all of it's blades, and they must be complete and not missing any parts.

And of course the inside of the radiator, engine, heater core, and all related tubes and hoses need to be clean and the coolant that is in it needs to be in good condition and not more than 50% antifreeze.

Of course if you have a high performance motor or do lots of high speed driving, then you probably should consider mounting an additional radiator in the airflow.

As for the PBS or FWD waterpump, I think they are great. With only one belt, it's failure is almost non existent. The pumps move plenty of water, so there is no problems with coolant flow even with two radiators. However, because coming up with an aftermarket cooling fan for the rear radiator that pumps as much air as the stock fan is basically impossible, an additional radiator mounted in the air flow is a must. Even for in town driving.

On the 850 application, the coolant flow at low RPM can be a problem as the FWD or PBS pump is originally designed to operate in a clockwise direction of rotation. If you spend a lot of time idling or driving around at a low RPM the car will run hot. My solution if you do not want the cooling fan on most of the time is don't do parades, drive around in a lower gear and higher RPM than you might be inclined to do (especially if you are used to American iron), and drive faster!

An alternative is to make an impeller with straight or directional blades for the anticlockwise rotation (I have done that before for customers with the 1300/124 conversion) of the water pump. But in my experience my customers have not had problems and have not needed it. They just drive fast!

I wire the electric fan in completely on it's own circuit with fuses and relays as there is no existing wiring for an electric fan in the car. I also put a fan sender from a Fiat with an electric fan at the outlet of the rear radiator to operate the cooling fan automatically, and install a lamp on the dash to tell the driver when the cooling fan is on. I never use a toggle switch that the driver operates because invariably you will get busy looking and/or driving and forget, or you will loan out your car and get back toast.