Just realized that by using "MAC" in this forum I might have sowed confusion. I'm using it in the networking context:
http://en.wikipedia.org/wiki/Media_access_control
IE, "The layer that turns raw electrical signals into a buffered stream of protocol commands and data".
Ironically IDE (and SD, and USB flash) all use very similar-to-SCSI commands for data handling. It's interesting to compare the commands in the 5380 manual to IDE/Compact Flash documentation, and in fact also compare the microprocessor-facing hardware interfaces of the two devices. Seriously, if it wasn't for the sticking point of having to rewrite the driver it would probably be way simpler to design a hardware wedge that substitutes a Compactflash card directly for the 5380 in a Mac Plus than it is to have to pick it up on the SCSI side.