I remember being told 20 years or so ago that Igor Stravinsky used to compose with Robert Craft as an in-person assistant to play things together as they were being composed.
I also remember being told that it was awkward to have two pianos in the same space, so they had a special one-case, two-guts (and two-keyboard) piano constructed so they could face each other properly, or collaborate in the way they wanted to, or whatever it was.
Is there any truth to this? Are there any pictures of the instrument? My Googling on the topic didn't produce much fruit.