Set your front axle first. Work in the 5 degree king pin angle, use an "angle finder", or better known as a protractor. Then square it up to the frame by measuring at a diagonal from the top of the king pins to a fixed point at the rear of the frame. Use the same reference point on each side.

Then go to the rear. You'll need to set your pinion angle (start at 3 degrees, might have to swag a bit for rotation when you get a load on). Measure for wheelbase on each side, and square the rear with diagonals to a fixed point on the front of the frame. Double check the angles, squares, and wheelbase and adjust accordingly. Assuming they set the brackets in the correct places you shouldn't be bottomed or topped out on any of the adjusting threads.