[Jim Sims]

Forget about the PB blaster or other penetrating oils. These are the infamous "necked down studs" in these models. Heat the nuts cherry red with a torch and spin them off while they're hot - have the wrench/socket ready. Carefully chase the stud threads and use new nuts with thread anti-seize compound upon installation of the three- to-ones. Some go as far as heating the heads at the stud base and removing the necked down studs and replacing them with normal cross-section steel studs. Chances are you'll break a stud despite these measures but good luck!