His plan was to mount them to the sides of his chair so he could type with his arms hanging at his sides. I don't recall if ever got past using just one of them, and actually, I'm not sure why he needed two in the first place. Now I'm doubting my memory. Anyway, more on this innovative keyboard:
That looks quite a bit more spartan than these chara corder keyboards I saw in use recently: https://www.charachorder.com/. They have a QWERTY keyboard with chording firmware (and a chip for custom keyboards) to try corded input for those who want to experiment without going all in.
I think that has more to it as it's not just chorded but has a steno dictionary as well. There must be a way to turn a standard keyboard into a chorded one?