In reply to Doug, Al, jcw:
This all sounds vaguely familiar! My recollection - autumn 1983 - is of four pitches from the lower tip of the Rognon to the top-out on the Plan-Midi Arête; each pitch was probably rather less than a full ropelength.
First pitch - mostly still on ice - followed the lower edge of the rock up leftwards to below a groove.
Second pitch went up the groove to a small col/ledge where the rock crest abutted the face above - quite possibly the feature that Albert's picture is looking down on.
Third pitch followed a line of pegs up the wall above and possibly slightly rightwards, then traversed up right to a constricted stance in a left-facing chimney/niche; presumably Al's sentry box. By this time it was dark and cold with snow flurries and a rising wind, so I was none too choosy about precisely how I used the pegs; so I'm in no position to suggest a UK tech grade or make a comparison with the harder bits on the Walker.
Fourth pitch followed a rising snow band/ramp back up leftwards - presumably a banked-up ledge or break; it was a vaguely visible feature that looked as if it might lead somewhere so I followed it. The angle soon eased and the ramp emerged abruptly onto flat ground on the Plan-Midi Arête.