I loaded a roll of HP5+ into my big mamiya press, which worked a lot better than the yashica. It'll natively shoot 220, so it can handle the long rolls and the pressure plate's correct for it. Produces pretty nice, wide negatives, slightly under 3x as wide as a normal 35mm shot.
Now scanning this is gonna be hard. I'm working on it now, and I think I can scan-shift-scan in my 35mm scanner and stitch them together afterwards. Which is gonna be kind of annoying...
It'd be nice if I could get vuescan to scan the whole length of the holder as one long image, and then see about 3d printing a holder without the between-negative supports. Or maybe like, one designed for this wild 24x90mm format. I so desperately wish I could just like script vuescan and put my own UI on it, that'd be so much easier for the goofy workflow I want, even normally.