http://www.geocities.jp/dental2l/memo/memo.html in Japanese only sadly.
Scroll down to below the Olympus Pens. Anyone familiar with this experimental "Leicaflex 18x24" (strangely named as its based on an M body)?
There is a picture of a "Leica Box" half-frame camera in Lager Vol. 1, but this is one I've not heard of before.