How was your axle supported when you tried to drive them out? If they were hanging on the springs, there's no way they're going to come out. Put a STURDY jack stand under the axle as close as you can get to the king pin and use the largest BFH you have. I would also apply some penetrating oil first, and maybe some mild heat (maybe up to 300F with a propane torch.)
I'm assuming you did remove the lock pins first.
From what i understand, 3/4 ton spindle bushings need to be reamed to fit the king pins after installation in the spindles. 1/2 ton spindle bushings drop in and don't need to be reamed.
