Got an impact wrench? That will take it right off. You can use a big
crescent wrench or anything to hold it when you tighten it back up. The
pinion nut should be available at your Ford dealer, but most people
reuse this nut, even  though they say you shouldn't. Personally, I'd
buy a new one. As you probably know the seal can be purchased anywhere.
You might ask at a NAPA store for the nut. Some of the other chain
stores will probably not know what you are talking about.