I was not able to find what EUB he was using.
His website lists this gear today:
http://www.stanleyclarke.com/gear_pg.htm
Today he's using his Spellbinder strings:
http://www.spellbindercorp.com/index1.html
However, knowing the kind of tone he has on upright, you can't go wrong if you get Thomastik Spirocores strings.
For easier playing, you may want to look at the Weich (light or soft in german) gauge.
He has been playing on LaBella strings for a long time. (and my guess is that these Spellbinder strings are actually made by LaBella...)
The LaBella models you may want to look at are the 7720M, 7720L and 7720S.
Medium, Light and Solo (extra-light) gauges, respectively.
Not many retailers are keeping LaBella upright strings though.
JustStrings.com have them.