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I don't know with any authority about a 64, but I suspect there would be more involved than just reboring the king pins, like king pin inclination, spindle boss location and spacing, steering geometry. If no one makes a kit with your desired spacing for your truck and you must have disk brakes, seems it would be a lot easier to use a kit with a different spacing and redrill the hubs and hats to the desired lug spacing, or use adapter spacers to change the pattern.