http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0311.htmHave you checked the toe in/out adjustment. You need a helper and a tape measure. Roll the truck forward at least one tire revolution. Pick a spot about 8" to 10" off the ground and measure across the front and rear of the front tires. The front should be 1/8" less then the rear.
Tire wear can be caused by a lot of things, loose king pins will wear the inside edge of the tire. Toe-out will wear the inside edge, toe-in will wear the outer edge.
How does it drive? straight, darts around, hard turning????
Bad Camber angle is caused by loose king pins or bent axle. Think of Camber as point above or below the truck that tires point to.
Toe in/out is a point in front or behind the truck that the tires point to.
Read the shop manual link I have added, it may help you pin point the problem.
Joe