The reason they're also saying you may need a saw is that if all that buring, prying and hammering does not break the bolt free from the sleeve, you'll have to cut the bolt because the sleeve will not come out through the smaller hole meant for the bolt only.
And yes, sometimes they're so rusted in there that nothing you do will free it up. But the air-hammer is a good start!
Prying certainly can help, but if it's really rusted in there, you're just expending a lot of personal energy and probably prying for nothing. I like prying and hammering together too, but it hasn't always worked on shackle bolts.
I'm sure you figured out by now you should have new shackle bushings handy, if you don't already.
Have fun!
Paul