SCSI Disk Mode was conceived by the Outbound developers. The implementation differed from Apple's, but it was the same idea. At about the time the Portable was launched, Outbound had settled with Apple for a legal supply of ROMs (yes, that made them a clone manufacturer) in an intellectual property swap.

A small French company offered a SCSI disk modification around 1990 for non-disk mode Macs. The information is around here somewhere...