Soak down the bolts with some PB blaster or other good penetrant oil and be sure to hit both ends of the bolt. The tip of the bolt actually sticks though the threaded hole in the unit bearing and rusts. But I've always been able to unbolt them this way with no problems. Getting the unit bearing out of the knuckle, however, is a whole new problem. There is a method using the steering system to push the assembly out described here: http://stu-offroad.com/axle/unitbear...tbearing-1.htm
and this usually works on all but the worst stucks. I have had to use a chisel to get out some badly rusted ones.
When you reinstall it, there is no need to spin it, just torque it down. You will most likely need to have the Jeep on the wheels on the ground to get it to hold in place while you torque it.