Having printed it, I see that the production spool bracket is to be placed vertically in place of the current (horizontal) penultimate spinal vertebra. Insodoing it leaves more space for a wide spool. It just occurred to me (sorry, I'm slow) that perhaps the spine a s is, provides not just guidance to the nerves and sinews of the box, but important flexural support (stops the large back panel from bending). Is that true? So I brought the Z axis down the bottom, and it looks as though the arch of the chain is such that the removed vertebra could just be flipped to the inside of the box when a production spool is in place, and work in parallel with (or more strictly, perpendicular to!) the replacement. Photo below: you can see the nuts of the spinal element that could be brought to the inside. Is that a dumb mod?