Greg,
the width of Normal 8 is the same as the width of Super-8 stock. So you can run Normal 8 stock through a Super-8 gate.
Now, if you do not use the transport pin of the film gate (for example by utilizing the Kinograph concept of transport rolers and independent sprocket registration/detection), you can simply use a Super-8 film gate for Normal 8, without the hassle of milling away anything, to capture the surrounding area of a Normal 8 frame.
Of course, that approach will not work if you are planning to use the transport mechanics of an existing Normal 8 projector, as the sprocket position is different from Super-8 stock.
However, the standard projection window of a Super-8 gate is wide and high enough to show you a single Normal 8 frame with surrounding screen estate. Your camera will also see part of the Normal 8 sprocket (compare the Wikipedia image you posted above).
There used to exist projectors which handled both Super-8 and Normal 8 with that “trick”, simply masking off the wider screen estate of Super-8 material in the case of Normal 8 film, and adjusting the sprocket pin position and movement accordingly if you switched format.