Corner drive? Is that a Canadian term?
I don't remember what kind of bus that Bob is working on, but if the fan mounts on the box, it is not the miter box like on the back of an Eagle. The GM 4501 used a right angle gear box with a shaft drive on the input and the fan mounted directly on the output shaft. If the correct name is so important, maybe somebody with a 4501 parts book can look it up.