C bushings are there to allow the suspension to move at all. If they weren't, your front axle and radius arms would be a solid torsion bar like a giant swaybar. Pinion angle and caster angle are directly related, when you change one--you change the other (with C bushings and link mounting points). You can infact buy degree'd c bushings for adjusting caster after lifting a vehicle, but they also change the pinion angle and noone makes them for something that tall. I don't know what stock caster is, but it won't be much. With larger tires and lift, you want 5-7*. With 12" of lift-- a, you're going to be too tall for anything. B, you're going to need to lengthen or drop the radius arm mounting points (or both). C, you're going to have to cut and turn the knuckles--having done it on a kingpin 60, I can tell you that it sucks pretty badly--to keep the pinion pointing in the right direction and the tires pointing straight. And D, You're going to have to figure out some sort of drag link and tracbar setup that doesn't end up with you having a Z shaped drag link.
