Well, you can do it! but its a little bit involved. One of the big vendors, I think it was southwest wheel had an axle package deal, 3k for a pair of 12k disc brake axles, springs, equalizers and everything to the door. Someone else up north had a killer deal on tires and wheels.
Spring perches moved out 2 inches
Space made for a spacer
Spacers made from DOM tubing turned to be an exact match for wall thickness
Stretch installed, I held the tubes square with 8 clamps on 2 pieces of 4x4 I beam clamped on either side, root pass of 6010 and a little hot, 7018 built up over that for 3 passes. Not the prettiest welds I've done but decent. Preheat was done with a big propane weed burner to keep the warping under control. When I finished there was a small deflection in the axle, that was fixed with one more weld.