http://www.boeing.com/commercial/aer..._07/index.html
Try this, all good stuff and from the manufacturer. The previous edition contains the start of the explaination on cost index and the two articles relate cost index to LRC. Some of it is a bit generic but if you want max range go for CI = 0 and not LRC, try it, it does make a difference.
Also interesting is the fact that LRC equates to 35 in a 73NG and 25 in the classic. It also gives the speeds that the FMC will fly referenced to head and tailwinds.
Another good source on information regarding this is the Bulfer FMC guide.
Hope the link works! PM me if it does not, or just go to the Boeing website and the commercial section looking for the aero publication.
