Personally, I hate using a chisel in a situation like this.
I have a set of sacrificial bolts for just this application. Remove the 3 original 12 point bolts and set them aside. Thread in the sacrificials (you'll only need the 2 lowers) and leave 1/4" left. Use a Ford wrench (sledge hammer!) on the heads. Yes, you *WILL* mushroom them, this is why you use sacrificials.
Goober up the mating surface with Never-Seez when you reassemble it.
BTW, torque on the axle nut is 175 ft./lbs. Have a BIG torque wrench handy.
NotoriousDUG has similar method that I haven't tried. It uses longer sacrificial bolts. Thread them in, and use the power steering to pop the hub loose by butting the sacrificial bolt up against the inner C of the knuckle. GENTLY! I suspect that it would be very easy to jam or bend on.
The MadXJ site has a good write-up for doing most of this.