You are doing it the right way around - activate using a OS3.9+BB1&2, then install BB3. But this is off-topic, so post in that thread you created in the ClassicWB forum.
The file "Devs/scsi.device" isn't part of a OS3.9 install.
The file in a OS3.5/9 install for updating the scsi.device is called "Devs/Amiga ROM Update".
Unless BB3 is meant to add a new scsi.device to Devs:???? EDIT: For "LBA48 support", it would have to patch or provide a replacement.
Last edited by Bloodwych; 16 January 2010 at 02:06.