You take the old fan off the pully and that's it. Click on my car domain, I have a how to for removing the stock fan on the 3.0's and a e-fan install how to.
Not sure about power, someone else can answer that question.
Many of us got our fans from Jusnes.
Here are some more benefits listed on the site.
* better GAS MILEAGE
* smoother and quieter running engine
* MORE POWER, without the parasitic loss of your old mechanical fan
* less wear and tear on the engine and water pump
* A/C cools faster in the summer
* engine warms up faster in the winter