My submissions used the Famicom art but kitbashed into the common vertical NES size and orientation of other 3D box art. The interests of a collector would probably be in some greater level of accuracy where the normal dimensions of famicom boxes are use. However, many of us have an interest not in separating Famicom from NES, but finding a place for the English translations that best fit the NES category.
My suggestion would be this. FFII (Famicom/Japan) would optimally get 3D box art according to its Japanese distribution:
Famicom box
That would optimally be scraped as the primary 3D box art. But for the quirky interests of the translation keepers (in effect a rom-hack, but not really, kind of?), the option of 3D box art that has NES dimensions for pleasing aesthetics and congruence with the rest of our NES collection:
NES "Box Art" Final Fantasy III
As for categorizing it, maybe the fact that I called it "Final Fantasy III 3D Box Art" but "North America" is a sly compromise as the NA release doesn't exist.