there's no spring missing at the back. The two springs present give enough tension to firmly hold the filmholder.
The focussing rod is on 4mm, the next bigger size available was 8mm but I found that rather bulky. I must say that the 4mm needs too much of turning the wheel.
6mm rod would be perfect, I think, but rack & pinion focussing would be even better!
the bellows is also home made.
they are souped in Rodinal, but I didn't print them yet. The negs look nice, except for some exposure errors due to the weird f-scale on the Zeiss/Compur lens/shutter combo.
I learned a lot from using my previous model. Mostly in usability: it had a bulky back that was a pain to switch from portrait to landscape, not enough redundancy in preventing light leakes and was too heavy and large to take on a trip.
I field tested the cambara II last weekend and encountered the need for a truly folding camera. It is possible with a slight adaptation of the back-to-bottom attachement.
As I just got (well... bought) a 8x10 film holder, that will be my winter project. I'd love to make contact prints of that size!!!