Over the whole period from 1953 to 1982, there are only seven different box sizes in total, and from the F type onward only three of them were still in use - three different widths. These two are the intermediate and wide types. Actually, even the (Superfast) G type boxes for this model come in the same two sizes, which I had known before. Therefore it is surprising that they made the same modification twice. I do not know the reason either. The narrower boxes are just wide enough for the model, but it can "breathe more freely" in the wider ones.