Disconnect the two antenna cables attached to the Airport Extreme card.
Apple was kind enough to include a label showing where each color antenna cable plugs in - just make sure to look at this when reconnecting the antenna cables.
Just successfully completed this repair. The guide is absolutely spot on with very clear high resolution pictures. I was working very carefully through each step and had no issues at all throughout the process until the very end when I couldn't find the last screw for the ram cover. Luckily it was stuck to the magnetic MagSafe charger port on the side of the I/O board!
I personally would rate this as a moderate repair instead of a difficult one as there is no specialist skills required like soldering. Thanks again!