Idea of new pluging.

[Nova]

You can achieve this effect somewhat by using ggalien's fit-on tool. Select the largest face of your source object, then select the face of one of your cubes. You'd have to flip the object according to the target face though.

Another, and more accurate solution to what you want is to use Wings' built-in bounding box tool. Select your target cube, then go Tools>Bounding Box>Save Bounding Box. Then, select the object you want to move/scale and go Tools>Bounding Box>Scale to saved BB>All and then Tools>Bounding Box>Move to saved BB>All.