I just called and spoke to Dave, and he says he did it a different way.
You can measure the width of the frame and compare that to the spring hanger, but instead, what Dave does, is he welds on the front hanger, bolts the leaf springs on, bolts the shackles on the springs, and then over the frame tubes. Then square the leaf springs up to the front spring hanger, and where ever the leaf springs position the frame tubes, weld them into place after you remove the shackles and bushings.
BigMike