You'll have to watch out with some U320 drives. Some U320 drives won't work in single-ended mode. Most are supposed to work UW, but SGI O2 owners have found out the hard way that that is not always true (I have an O2, and a later-model 300GB U320 drive worked fine in it, but I did my homework first). See the Nekochan O2 Hardware Aggregator post's FAQ entry 1a on the subject.... (
http://forums.nekochan.net/viewtopic.php?f=3&t=8113 and you'll have to scroll down to it).
If you can get a 29160 or 39160 series you'll be a lot happier. These cables show up on eBay a lot; you do need to get an SE-compatible cable (most LVD cables are, but I have one or two here that aren't; look specifically for LVD/SE on the description) for the 2940UW. Something like:
http://www.ebay.com/itm/Amphenol-497330001-Ultra-2-Ultra-160-Ultra-3-Internal-SCSI-LVD-SE-Cable-/252692840930?hash=item3ad5aac1e2:g:yQ8AAOSwOyJX5WhG should work ok.