i had the bung from a b11 sentra/sunny added to the older radiator in the same position as the sunny rad, lower right corner, yeah it doesn't trigger as soon as hot water comes out of the engine, but not sure you want that.

Having a switch that lets you force it on manually is good, but you don't want that as your only way to use it.

USE A RELAY!!!! or you will burn up the switch in the radiator and your fan will fail and piss you off..

if you can keep it under 100C then that is a good thing, you want it to get warm enough to get the oil to it's state change, and cook out the gas condensate, but there isn't really any benefit to letting it get warmer. A benefit to not letting it get up to 100C is hoses never burst, and you can drive home on a leaky radiator in a pinch.