I was wondering the same thing when I got it. I have the 4.0 and the new fan is about 6" smaller than the radiatior all around. First I mounted it with the supplied brackets on the top and zip ties on the bottom, wasn't satisfied. I used my skills, and took the old shroud and fit the new fan into it. It fits real well. I put the new fan on the ground, set the old shroud over it, only an inch or so extra space and the given spacers fit in there nicely. I drilled holes on the shroud where they bolt in on the proform. Bolt them right in. I'll try to get pics, i'm moving in to college at the moment but when i'm done i'll have some time.
The e-fan gave me a nice amount of noticeable power and torque.
Gas mileage, I got at least 2mpg better than previously. My tires are 31's compared to stock 29's and I never got my stuff recalibrated, so the mpg is off by a few, I probably got more than what it says. It's definately worth it.
I got mine off of summitracing and all of the necessary wiring was included, didn't need the brackets at all. You don't need anything extra.