I have a page for ivan’s cameras in the tech galleries – http://www.cdags.org/?page_id=610
the stereo attachment with 6th plate camera in action can be seen at the bottom of the page.
Also there are a few variations on this design – can be seen in vintage examples at
http://www.cdags.org/?page_id=285
Ivan does amazing work – fine dovetailing and design. He does machining of brass to make flanges for lenses and other metalwork. His cameras sometimes come up at the Christies camera auctions in London with the vintage material. I heard of camera collectors getting him to make sliding box cameras without the hole for the lens as apparently this was how they were bought in the 19th century – you then choose a lens and had it fitted.