I'll tell you guys one thing I've learned just very recently about pulling pitman arms off steering boxes--I pulled three; two off a '62 Corvair, the other off a '60 Chevy truck. Both of the steering boxes were off the vehicle.
On the first corvair box, I tightened down the puller, banged on it, heated it, etc. etc. and after a LOT of work, it came off.
On the second one, I held the box in a vise and tightened the puller up pretty snug, and then a bit more, and walked away from it. After about two or three minutes, it popped off on its own.
I did the same thing with the truck steering box--tightened up the puller so it had some tension, but not enough to deform either the box's shaft or the puller, and walked away from it. After a few minutes, the arm popped off and landed on the floor.
Slow, steady force seems to do the trick. (I was using an big, old Bluepoint 2-jaw puller--not the best tool for the job, but it's all I've got)
-Brad