I did this upgrade myself. The PDF guide they provide have you doing it from the top of the engine bay, but I did it from the bottom and it was super easy.
I have done two "spirited" driving trips from Seattle, WA to Napa, CA with the pullies with no problems.
Here are two links that I read before I did the work.
http://forum.e46fanatics.com/showthread.php?t=177459
http://www.bimmerfest.com/forums/sho...d.php?t=141297