[jpstewart]

AFAIK, it's 50-pin SCSI but on a 2-1/2" drive instead of the more common 3-1/2" form factor.  (A few models of laptop also used that SCSI form factor.)  The connector used a 2.0mm pin spacing instead of the usual 2.54mm (i.e., 1/10") spacing.

If it helps, the Sun Field Engineer's Handbook says Toshiba MK2326FB (340MB) and MK2328FB (810MB) were the supported models.

There's also an adapter available on ebay: https://www.ebay.com/itm/270840619638 if you can't find 2.5" SCSI drives.