Looks like it has the Nervar crankset with guard, which was much better executed than the Stronglight "3-ring" double since it has a much more-symmetric Q-factor.

Judge the frame by the joints and alignment. Many G.S.'s have truly substandard brazing hygiene and alignment that is obvious to see and which compromises integrity.

The oxalic acid or vinegar soak (using soaked towels wrapped around the tubes and joints) will remove the rust. Do this before doing any sort of mechanical removal steps! The frame will look great (and should ride great) if the joints were brazed by one of the better factory hands.
I never understood why people so often clamped the bottle cage over the transfers.