At least it would probably make some interesting context for the Russ book.
It's a shame that it's out of print. I don't even have a copy of The Clewiston Test myself -- I'd read one I borrowed via an inter-library loan. If you can find a copy, maybe you could hand out a paragraph or two to your students. Perhaps from Anne's husband's point-of-view, to a comparison to Ernst's point of view. I'm sorry I can't give you any quotes from it.
Another intertextual connection would be the Suzette Haden Elgin short story "For the Sake of Grace" whose premise Russ borrowed for her novel -- I haven't had a chance to read it, though, because it's even harder to find.
But I'm rather happy for The Two of Them to have been your choice, if only by default, because it makes a change from the singular focus on The Female Man that usually leaves the rest of her work in shadow. (ObHow To Suppress Women's Writing...)