There is a product that converts an Apple HD-20 into an SCSI device. Available
from Personal Computer Peripherals Corporation, it is called HD-20 WSI.
The HD-20 WSI is an upgrade for the original Macintosh HD-20 that allows it
to interface with the Macintosh Plus, Macintosh SE, and Macintosh II via the
SCSI port. The HD-20 WSI modification provides users with significantly faster
access to the data stored on the hard disk.
The modification consists of a plug-in circuit board, interface cable, and
utility software. The circuit board uses the existing HD-20 connectors and
requires no soldering. The utility software includes HFS Backup, Eureka (a file
finding application), a floppy disk copy program, and ImageWriter/LaserWriter
spoolers.
For more information, search under: "Personal Computer Peripherals"