Hi Dougal, I have a similar GVP SCSI Card in an Amiga 2000, it is fussy about correct termination.
The SCSI chain should look something like this:
Term, Hard disk, Controller, Term.
The GVP SCSI Card should have auto termination for the end beyond the controller, so you'll either need a terminator for after the hard disk, or set the termination jumper on on your hard disk if availabl
Hope this helps and your setup goes well, SCSI Can be a pain but works nicely if setup correctly, be patient and don't panic if it doesn't go right the first go.
Robert.