Between brakes (1.6mm) and shifters (1.1-1.2 i've seen listed) the thickness of the cable is slightly different and the housings are definately different in function. Shifter cable housing is compressionless or somesuch.  
Here is the gospel from Shelton Brown to tell y'all about it.
http://www.sheldonbrown.com/cables.html
 
Key Warning
"Warning: Since compressionless housing relies on plastic to hold it together, it is not as strong as conventional spiral housing, and should never be used for brakes! The loads applied to brake cables can easily cause compressionless housing to rupture and burst, causing a complete and sudden loss of brake function."
 
edit: Not sure about the bike in question but I know most of my bikes require tandem length stuff.