I've made two sets now on my own (well, one set still needs finish welding). Both times I didn't work off a specific length, I just set it on the truck. Jacked up the front, supported the frame on jack stands, took the tires off and went to work. Both of mine I built the mounts and attached at the transmission cross member. Cut the existing arms to take 2"x2"X1/4" square tube and removed the stock mount. Positioned the square tubing, positioned the front axle, clamped, tacked, then cycled the suspension to make sure it was how I wanted it and welded it up.
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