So after a few more hours of tinkering this evening I noticed there was a ton of play for me to twist the axis. Taking a look at the roller assembly I saw that in all the pictures your rollers were staying upright on their own, whereas mine were too loose to do so. I’ve since tightened them up and there is hardly any play at all now.
Having done so, after disassembling and reassembling the middle assembly, and I put in the Z axis after installing tension bolt C as instructed. The picture below is the end result. One point I have noticed is that the problem areas are in the top-left and bottom right corner, with the former being too close and the latter being too far. Would this imply that the middle assembly is, indeed, square and that my issue lies with the base?
thanks for your insight so far!