Take a closer look (2)
I had a 7-speed hub and an old Alex rim lying around, so I built a wheel this morning. When I had the wheel finished, trued, and dished (I use the old gaspipe frame to center the wheel,) I was sitting there looking at the short freehub when I realized that it would be simple to pull an old Sram PG-850 apart (I have one of them sitting around as a leftover from when I converted the mlcm to a 9-speed, and I already knew (from one of them disassembling during a brevet) that they were easy to take apart) and see how well it would fit.
To make a short story short, if I take an 11-32 cassette and pull off the 32t cog + spacer, it’s almost exactly the same width as a 7-speed cassette. It’s a little narrower, but the 7-speed freehub I’ve got (a Shimano R050) is narrow enough so I can tighten up the lockring without it bottoming out on the hub. I lose the little bolt that fastens the cassette together, but I’ve a hundred miles or so of brevet that tell me that it works even if the lockring is loose enough so that the cassette jingles like Santa’s sleigh.