The couple frames I boxed we used long pieces and cut them in the shape of the frame. Then welded to the inside of the rails, with proper clearances and a good weld all you have to do is clean up the edges. Think of it more of filling in a gap over a butt weld.

With a frame shorten we have always ground a V into the plates that get butted together and fill the area, grind back smooth. From there we would either put a plate on the inside for strength or a diamond shaped piece on the outside. In one instance we actually did both. Another time we just boxed that little section of frame and it was good to hand the fuel pump and remote filters on.

Most of the body mounts would be in the same locations, might have to move a couple for the extra on the bronco body. But not that big of deal for that.