Detail of the S-IVB's hydrogen tank wall, just aft of the forward skirt.
In this view, the mount points for the auxiliary tunnel are clearly visible.
Also, I assume that the two distinct circles visible through the scaffolding,
plus the to circles partially obscured by the right and left vertical beams,
are the mount points for the cold helium sphere mass simulators.
This is S-IVB-D, the dynamic test stage. If this were a flight stage (or even
a more flight-like testing stage), I would have expected to see the cold
helium line running from the auxiliary tunnel to the forward skirt.
However, the Model
Specification, Saturn S-IVB-D Stage reveals that each cold
helium sphere on that stage is simulated with a "dummy mass," so the stage
lacks the plumbing associated with the propellant