Ah Ned that's interesting. You use the same slot for the paper negative and the darkslide, which is a marvellous simplification that hadn't occurred to me.
Constructing "picture frame" shapes to build a holder uses a lot of material - I think I would need 3 sheets of A3 per holder as a minimum (for a double sided holder). If one treats each side of the quadrilaterals as a separate strip, it's much more efficient (one and a bit holders per sheet), but needs more thought and of course is more fiddly and prone to error.
Mark that's a nice looking camera. Thanks for the link. I'd like to have a go at something similar one day. I actually bought the Greene book the other week but then sent it back in a fit of buyer's remorse. I'll keep my eyes open for a second-hand copy I think