It's been awhile since I worked on a hinge pillar, but I'm still of the mind that a 2x4 and a sledge hammer would move the pillar in place. If your concerned about how far to move it, take a straight edge across from the other door/pillar for comparison. Your mockup looks good and would do the trick, but then you have to contend with cleaning up tack welds and possible damage to the metal around the hinge pocket. The 1/2" gap your refering to, is that between the cab corner and the door? Pic's would help out a lot.
