For the hub, the distance from freewheel stop to the end of the locknut needs to be a minimum of 40.5mm. Try to achieve the minimum - not more - for the reasons already noted by others.
That will qualify the hub for an 8-speed freewheel...
=8-)
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5000+ wheels built since 1984...
Disclaimer:
1. I do not claim to be an expert in bicycle mechanics despite my experience.
2. I like anyone will comment in other areas.
3. I do not own the preexisting concepts of DISH and ERD.
4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
5. My all time favorite book is:
Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life