In Wings3D:
1. Right Click then select "Cube"
2. Select entire cube, Right Click then select "Scale" then select the top choice in the sub menu.
3. Scale up accordingly. To check the size switch to the "node" triangle (the furthest left triangle in the upper menu bar) then select the top two corners of the box........in the upper left corner of the screen you will see the "information" It will tell you what "vertices's" are selected and the distance between them.
4. Scale it up or down until the distance is what you want your final wingspan (in inches) set at.
5. At this point in the Geometry Graph set the BB to "invisible...or see through so only the edges are visible.
6. Now place your top view of the 3-view plans in place.......scale that up the same way until the tips of the wings are at the edges of the bounding box.
7. From there you can move the top or front of the BB in or out to match the front, top, back and bottom of the 3-view plans if you want. But the Wingspan distance is the only thing that matters.....so this is an unnecessary step
8. From here you won't need t BB anymore