Prepare to spend a lot of time on this step.
As you can see, I pulled out the Bernz-O-Matic propane torch for the step and headed up the nut bolt to make it a little easier to loosen this nut. Spend about 3-5 minutes doing this, got to the next step. If it still won't budget, heat it up some more. You may try some penetrating oil like JB-80