I've checked the source, and the sbic driver appears to treat LUNs properly -
a device with multiple LUNs will have all LUNs found.

Can someone more knowledgeable confirm this?

The reason I ask is that the Sun3 port also uses /sys/scsi, and the Sun
si driver is finding my Quantum 105 at multiple LUNs.  The Quantum was
previously in my Amiga, and the sbic driver found only one LUN, as it
should be.