The included notes mention various exposures you should use when duplicating different types of film, though, and from that you can calculate roughly an equivalence of ISO 6. Further complicating the situation, this stuff expired in 1985, about 30 years before I actually processed it, and nobody knows how it was stored all those years.
So I did something different, and actually bracketed my exposures and took careful notes of each frame. I used the Leica M3 and 50mm Summicron to expose four sets of five frames, changing the aperture one stop between each frame, with the middle exposure of each approximately where I thought a "proper" exposure should be given ISO 6. Getting exactly that exposure was complicated by the fact that "6" isn't a full stop equivalent, the sky outside that day was mostly sunny with some wispy, intermittent high altitude white clouds, and that I have no idea what I'm doing.
As for developing and scanning, I used North Coast Photographic Services in Carlsbad, California. They developed the film with standard exposure times using E-6 chemistry (as proscribed), and scanned on a Noritsu Koki scanner, which automatically tries to correct under-exposed slides. Anyway, here are the results. My "ISO" rating on each photo is educated guesswork, based on exposure settings, subject, and level of sky cover.
Based on these results, I'll shoot my remaining rolls of ESD using an exposure equivalence of ISO 10 to 15, really bringing out the strong, dark colors, and giving the photos a slight underexposure, which the scanner can correct for.
And finally, here's some of the better shots from the remainder of the roll.