Another place to look might be navsource
http://www.navsource.org/archives/08/04idx.htm
It looks like it will either list the fuel capacity or range for most.
edit: Considering so many boats were modified individually, I would imagine one exact number probably wouldn't apply to all boats. Some will be higher or lower within the same class.
edit2: just looking at early Balaos vs late ones, the earlies have around 95,000 fuel capacity and the laters have around 115,000 or so, so one number won't sum up all the boats in a class.