DOVE MacSnap SCSI adapter / looks exactly like the John Bass schematics, though with a few more resisters and capacitors as well as terminators
Scans?
Charlieman has some good shots of them on his site:
http://www.vintagemacworld.com/macsnap.html
is extracting the routines from the 128k ROM and inserting them in the startup System an option?
I've been ruminating on that very issue. I think the problem is that even if it were possible to extract the SCSI resources and properly insert them into an earlier system, the 128K ROM has a startup routine that tells the Mac to look for the SCSI devices on the chain. Even if these drivers were in the System, they would load after startup, so that routine would not work to load the HD, and would still require some kind of drive mounting routine added to the FInder. I'm sure there's more to it than that, but it's worth a look I suppose.
