MicroVAX 4000-105 Fast Wide Differential option?

Today I came across an oddity, a standard ds-47dbm-b9 VAX 4000-105A but seemingly featuring a third-party FWD/DSSI/SCSI option. Instead of the usual angled rear connector box containing 2 DSSI busses and a SCSI-1 connector the machine had a rectangular breakout box that featured from top to bottom FWD SCSI (68pin), blank, DSSI (single port), SCSI-1. The FWD port was connected to a Baydel RAIDER5 raid system and also had a differential terminator. I'm pretty sure that wasn't a DEC option in the UK, 2 DEC resellers I know agree so has anyone else heard of this? I wasn't allowed to shut the machine down so I couldn't check for manufacturers or part numbers..... VMS designator for the drive was DKW100 which further points at it being wide SCSI.... cheers! adrian/witchy