I just got a fat Childcraft catalog from 1974, and it's fat with interesting toys and kids' furniture.
Like these Nesting Chair Blocks, for example. Cube-shaped chairs are classic, even basic. But the idea of using multiple chairs as modules for building seems really fresh.
And the best part is that cranking some 12" cubes out of 5/8" birch plywood seems really straightforward. You'd want to round the corners, but you wouldn't really need the handle cutouts. Unless they had little inserts that helped keep a structure made of chair blocks from instantly sliding apart.
Previously: Nomadic Furniture has plans for slot-together plywood cube chairs. And of course, Thomas Maitz invented them again with his Max in a Box.
And this 2003/04 habitat lock table/Chair looks really familiar too :
http://storage.canalblog.com/51/28/502285/37559107.jpg
Discovered this specific post a couple of days ago and added the link + picture to my post with a link to your flickr page.
And since it's the first time I am posting a comment, just want to mention that you are doing a great job! Very inspiring and knowledgeable.