Carried over from the other thread, it looks from the photo that your 120 holder could be turned through 90º but then the actual film strip would have nowhere to go. Someone adopting a similar desigh could either fix the back board a bit higher or if they had access to a router they could rout a suitably sized slot for the film to go through, protected with some kind of soft material of course. The basic model of the Bowens Illumitran (i.e. without the Contast Control Unit so a simple upright support) had such a slot for 35mm film.
I’m thinking aloud here, for my own benefit really. Your lens collar easily facilitates turning the camera through 90º. Anyone using a bellows and an L39 repro or enlarger lens couldn’t do that.