My Vitus Carbone came with a Shimano DA 7400 crank and BB. IIRC, the spindle was 113mm long. I installed a slightly longer spindled (118mm) Stronglight BB to go with the Mavic cranks I got for the bike and it worked out good. The 979s and Carbones have pretty much the same BBs at the shell so I think a Shimano BB with the proper JIS taper on it and 113mm legnth should work if you are installing a Shimano 600 crank on it.
I don't know why a longer spindle would supposedly work better for flexy frames.

Chombi