You could do this with the Outbound Model 125 Laptop and the external SCSI Adapter.
The Outbound Model 125 allowed one to set the SCSI ID of the host (the Laptop) so that one could do the docked thing, i.e. attach the Laptop as an external SCSI drive to another Macintosh. However, if you exited the pretend-you're-a-hard-drive mode and booted normally, the Outbound would have access to all the SCSI devices on the chain at the same time as the host Macintosh.
I did this trick with my IIci and my Laptop Model 125 several times. That way you can give the Outbound access to the internal drive of the IIci.
Since SCSI Powerbooks also had this ability (I understand that Apple licensed it from Outbound) it might be doable with PowerBooks as well.
The Outbound Model 125 allowed one to set the SCSI ID of the host (the Laptop) so that one could do the docked thing, i.e. attach the Laptop as an external SCSI drive to another Macintosh. However, if you exited the pretend-you're-a-hard-drive mode and booted normally, the Outbound would have access to all the SCSI devices on the chain at the same time as the host Macintosh.
I did this trick with my IIci and my Laptop Model 125 several times. That way you can give the Outbound access to the internal drive of the IIci.
Since SCSI Powerbooks also had this ability (I understand that Apple licensed it from Outbound) it might be doable with PowerBooks as well.