Remove stuck shackle bolts?

I'm trying to replace the rear leaf spring shackles on a 95 chevy c/k1500. But I can't get the bolts out. I've tried PB blaster, turning them and hitting them as much as possible with what little swing I can get with a hammer in there, and I've tried pressing them out with a C-clamp. I really don't want to take the bed off. Is there any other way? anyone else done this?