Adding a Hard Drive to an Original IBM PC Using a Raspberry Pi
insentricity.com
insentricity.com
I got as far as 3.3v to 5.v interface logic, plus acquired logic analyzer traces of real floppy data patterns.
Alternatively the Printer port supported 8bit parallel transfers are was much much faster. Potentially a USB -> Parallel interface on the Pi. I remember using a Parallel to Parallel cable between 2 486s with the lap link software and getting MUCH faster then serial connection.
Pretty cool.
In that regard, Oric recently caught up with the C64. ;)
There the Pi end up acting as a terminal server (if i get the terminology correct) via a serial-to-USB setup.