Well, the advice that brianrupnow gave you might be a good idea... However, if you use a Mustang box (or Maverick) the pittman arm must point up. Another alternative is the Ford Ranger Pickup box which already works backward of the Vega and can be mounted with the pittman arm pointng down. The problem with the Ranger box in the way it mounts...

To answer your question you sent me separately, I can't remember exactly what the inside of the box looks like and don't have one that I can take apart to look at. What I do remember is that the bearings end up being located in the same place as before IN REFERENCE TO THE INPUT SHAFT. In other words, if there was a bearing under the bottom of the shaft when it was in the upright position, it will have to move with the shaft so that it is still under the shaft after it's reversed.

I wish I had a box here so I could take it apart and take pictures. I tried to answer your message direct, but couldn't get it to work.