Skybum are you referencing Olblue's brake conversion? He was definitely working on a dually front hub, and it is a hub not a spacer. I've seen his with my own eyes.
The only dually spacers I've ever seen are aftermarket items that I would not trust on a working truck. I suspect you are seeing the same thing everyone else does until they start taking it apart. The brake drum bolts to the rear of the hub. That gives the appearance that the outer portion of the hub might be a spacer, but in fact it is not.
Look at the outer bearing. If that piece is a spacer you need to replace the piece that mounts the bearing. That would make a single-wheel hub a two-piece hub, or mean machining something special.
Take it apart and look. If I'm wrong I want to see pictures. This comes up pretty often but so far no one has ever come back with pictures of a disassembled hub with a spacer.
