Are you sure they did not use 71-72 Chevy pu spindles for the 5-lug conversion. That is what I have always used for those trucks. They use the original control arms, but use different ball joints (I can't remember the exact difference). You might check that out. The easiest way to tell if you have the original control arms is to see if they still have the steel bushings (hex shaped parts in the shafts) instead of later model rubber bushings with washers and bolts to retain them.