It's all in the pb blaster and the hammer game.... Trying a straight on pull will never work, just rip the guts out of the steering box, or break your puller.
keep soaking the pitmarn arm and the steering box shaft for several days, and then hammer the hell out of it. 2 large hammers, one resting on the pitman arm, and smack the first hammer with the second, that's always worked on the jobs I have seen.
Another last ditch method is to use a die grinder and cut the pitman arm in 2 or 3 places around the shaft, that will help to give it some slop and come off.