If I'm not mistaken, ISE (=Integrated Storage Element) for DSSI just means
"disk", and it may be cabled internally, IE with ribbon. There are ID
selectors that go on the disk _housings_, but they may be skipped and
overridden with an on-disk jumper block, at least with most RF series.
Any DSSI disk should work The RF31 starts at under 400MB, the RF74
ends at under 4G. DSSI disks are getting rare, but are still do-able on
eBay. I've got some too.
Good Luck,
John A.