in my opinion (others may chime in as well) you need to do both front and rear since on a big bolt, most if your braking happens at the rear axle as opposed to a car or light duty truck where most braking is done at the front axle.
That said, 55 and earlier have the 5/10 lug setup, where in 56, they went to the 6 lug pattern. I may be beneficial if you are making them, to have an option of bolt pattern.
