It's not a striaght forward action as just mounting the drive - SCO has no SCSI mount information so the drive has to be configured in SCO SCSI tables before you can access it. It's a rather complicated procedure.
SCO site has a technical document regarding this. TA# 104863
It is intitled " How do I add a SCSI or IDE disk that has data I want to keep? "
It has step by step instructions for adding a drive.
Here is a direct link to the relevent document.
How do I add a SCSI or IDE disk that has data I want to keep?