He sent me one of the resulting PCBs, and I spent some time last night throwing it together, using bits from my junk box. Note the cool labelling on my TI TMS2793 floppy disk controller IC. The bit on the right comes off when scrubbed with isopropyl, revealing the writing on the left. It’s still a TMS2793, but with a HP part number. I wonder if TI was responsible for the relabelling way back when?