AFAIK, those are the LOX/GOX F/D and vent pipes for the Centaur LOX servicing system. While the LH2 was to be serviced through the Rolling Beam Umbilical System (RBUS) that was mounted between the RSS/FSS, the LOX was to be serviced through the LOX TSM on the MLP, through a dedicated F/D port on the LOX TSM carrier plate. The F/D system interfaced with an available pre-planned LOX F/D port on the orbiter that had been capped until then.
Thanks Dave for these interesting information and the drawing,
which I also have found in the Thread
The Shuttle Centaur (Reply #83) 
Do you know exactly when the supports for these pipes were installed on the
MLP-2?
