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Close-up of various components on the top of the engine (as it rests in the museum):

• To the upper right is the back of the engine interface panel.
• The large-diameter pipe under that (bending away from the camera) is the no. 2 oxidizer high-pressure duct; a bit of the no. 2 oxidizer valve is visible at the bottom of the photo.
• The large-diameter pipe bending toward the camera near the middle of the photo is the no. 2 fuel high-pressure duct.
• The heat exchanger occupies the upper left of the photo. The two bottom-most lines leading into it (leading to the two left-most connectors) are the helium (bottom-most) and oxygen supply lines; the two upper, larger-diameter lines leading away from the heat exchanger are the helium and oxygen return lines (it's hard to tell for certain from the pictures I took, but it appears that top/right-most line is the oxygen return and the one just below/to the left is the helium return).