Glad to hear you got the problem sorted. As been said many times, HD motorcycles use BOTH SAE & Metric fasteners and i.e. if you see what appears to be a phillips head #2 but has a round dimple next to the cross...it is METRIC (take a look at the front Showa fork oil drain screw). The impact driver phillips head is hardened and tighter fit and works (the handle by itself has plenty of leverage), but if you feel it is "camming out" STOP, and get the right fitting bit before proceeding. Save yourself a lot of grief.
http://www.hdtimeline.com/chassis_suspension_and_front_end/10500-frozen_fasteners.html
http://www.hdtimeline.com/chassis_suspension_and_front_end/10500-frozen_fasteners.html