I got lucky with my pitman arm, twice... (the second time don't really count 'cause it was only like 2 years after removing the stock one) My stock pitman arm popped right off with a crappy "pep-boys special" pitman arm puller, and no impact gun. (still living on the stone age, no air tools)
You may or may not be so lucky. If it wont come off with a puller and liberal amounts of PB blaster, brute force, and swearing (yes it helps)... your going to have to cut it off. Use a grinder and a cut off wheel. Only stop the cut BEFORE you cut all the way through. Once you get it cut most of the way it should pop off with the puller, or use a cold chisel to snap it, then use the puller. Even though your getting a new steering box, you may need the old one for a core. You may not get your core charge back if you cut into the splines of the old box. I don't know, but better safe than sorry.
As far as a steering stabilizer goes... (your going to get a bunch of recommendations, but...) the stock unit is all you should need! If the front axle assembly is in proper working order and the steering is also in proper working order, there is no need for a "beefier" stabilizer.
Running a larger stabilizer for reducing or eliminating shimmy, bump steer, or anything else that they are commonly "upgraded" for is putting a bandaid on your elbow for a sore on your knee. It might make the problem feel better for a bit, but the problem is still there. Fix the root problem, not the side effects.