I'm sure there are more knowledgeable on this subject than I am, but I can offer a few guidelines.
ON the Truck: You need to find and measure the center line of your wheel wells. That is the mating surface on your rotor and brake drum.
From that point you need document the distance to both the inner and outer fender from the Center Line.
ON the Wheel/tire: Measure the distance from the mating surface of the wheel to what will be the back of the tire. Subtract those inches from the overall width of the tire. (Assuming you have that data)
Draw out the rotor center line and fender distances. Draw in the wheel dimensions. You will see if you need spacers.
That's a start, now you will need to see if the tires will clear or Rub...
