Thanks. I should have thought of that. "As always, Sheldon has the answer."
I am not sure how to calculate the space savings from thinner cogs and spacers, and the increase from the additional cog and spacer, but I will work on it. As I said, I've done this before. Must get a battery for my Pep Boys micrometer -- too hard to read the gradations in "analogue" mode.
One "truc" that I've learned is how hard can you squeeze the plastic spacers to get the lockring to grab the tiny, little, first bit of threading on the hub body. Sometimes a different lockring will grab where another won't: the "Sunrace" lockring in my bag has an extra row of thread compared to the Shimanos, which is sometimes just enough to grab the hub body threading and allow you to squeeze it on and compress the spacers just enough to get non-canonical arrangements to work, as when I spaced out a 7 with two extra spacers at the hub body flange: a bit of leaning while turning was required.
The salient bit of information is the fully 2/3" difference in width between a 5 sp fw (23.2 mm) and a Shimano (40) or Campy (40.1) 11 sp cassette.