Thanks! 244 is a 74LVC244, which is acting here as a 5V to 3.3V level converter.

I think something like HD20 behavior is possible in time, though it might be easier to write an all-new driver for it than to reverse engineer the undocumented HD20 behavior. But I'm intentionally not thinking about that stuff yet... I just want to get standard floppy emulation debugged and working on the new hardware.