One additional point. The caption of the Western Railroader photograph of the GS4 pulling 132 specifically said that the train was bound for Los Gatos. The caption may have been incorrect, but it said it was doing the branch. Interestingly, the GS4 in that photo had it's cowling and Daylight colors. The photo caption mentioned that it was a misconception that commute trains never had GS locomotives pulling them before the cowling was removed and they were painted all black.

I probably still have that Western Railroader copy. It was published in around 1976 and had this feature photo essay of steam powered SP commute trains.