Chuckle, it's certainly on there tight. I've used both the allen key trick and a deep socket set on that bolt head and held in place by a rachet handle. Once the fan base is held undoing the nut can require a certain degree of persuasion; in my case a Lisle fan clutch tool and an air hammer. A bit of anti-seize might help in future removal and by the way no particular need to torque the nut on reinstall; just run it down until it stops as normal operation will add any additional tightening needed if any.
As to the # of bolts the FSM pictures I can find imply 4 and GDE's TC instructions (
http://www.greendieselengineering.com/f ... st/37.page) say 4.
PS if you are already in there with the fan off then in addition to doing the fan shroud mod I'd strongly recommend dumping the OEM fan clutch and replacing it with a Hayden 2905 (ca. $43 on Amazon with free shipping). It's a much stronger clutch and engages (as does the OEM based on air temp off the radiator) at a lower temp than the OEM which will catch an engine temp rise shortly after it starts rather than well after it's begun. The former is much more likely to stop/prevent overheating than the latter.