here's where things get really interesting. i've pulled in the imagery of the early ST-251 board and overlaid my Kicad traces from the newer revision.
it's almost like a visual diff--now i can see exactly what changes were made between board versions, which means i can back out a schematic as well!
well that was epic! i've completely reverse engineered this older revision. details in the repo (https://github.com/schlae/HardDriveInfo)