Side-mounted Spool Holder for the Original Prusa i3 MK2

I really disliked the original two-piece spool holder on the Original Prusa i3 MK2 and after printing a slightly different design (with a filament guide), I decided that mounting the spool on the top of the frame just didn't sit right with me. The PSU is a metal box with reasonably thick material, screwed into both the base and the upright frame of the printer, so I decided to use that as my mounting point.

The way of fastening the mount "plates" I used isn't ideal, as it's quite fiddly to ap