Just to prove that I have not completely lost my mind, this site states that balks were removed from LL in 1999. Granted, it's not a rule book but it's something.
http://mysite.verizon.net/rutherford.ll/umpinst.htm Scroll to the bottom under the heading, "Recent Rule Changes".
Same thing if you check here and look under "Game Rules".
http://www.davislittleleague.org/rules_aaa.asp
I will see if I can dig up a 1998 rulebook, I think I still have one.