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Overall view of where the removed auxiliary tunnel would have been mounted, on the side of the LH₂ tank and forward skirt.

Picture 2 of 2.

The four round holes under the auxiliary tunnel are presumably attach points for the cold helium sphere mass simulators. (This particular S-IVB is the dynamic test vehicle, which means that it was built differently from a flight stage, including the use of mass simulators in place of certain flight hardware; refer to the Model Specification, Saturn S-IVB-D Stage for additional information.)