I haven't seen the route in a guide book either and its a while back (25/1/98) but as I recall, it followed a line immediately below point 3760 on the SE side of the Midi. It was approached via a steep snow slope 250 mts SW of the line indicating the route of the Mont Blanc tunnel (Carte de Randonnee, Cham Mont
The note in my log reads "Pierre Rebuffat Couloir III/IV. Steve leading Lee and I. Great climb (v cold) hard overhanging crux with very poor sugary ice and
difficult thread. Struck by rock after abseil descent"
As an aside, I still have the rock (size of a half-brick) and I wrote to Camp on my return to UK to thank them for making an effective helmet! I was looking down at my belay device as I removed it from the abseil rope when the rock struck me on the back of the head. It had fallen about 60ft and were it not for
the helmet and the rolled up wired hood of my Snowsled jacket that cushioned the impact on the back of my neck, it would probably have spoiled our day. As it
was, it turned my lights out briefly and put paid to our plans to ski the Vallee Blanche. Another one of those memorable "learning experiences".
† This climb cannot be verified, and the crag moderator needs more information.