[Gordon]

Steve,
A picture is worth a 1000 assumptions, most of which I made were wrong.

I assumed there were only 4 valves in the 6 pack because with the 2 valves on the frame, no exhaust at the 6 pack would be needed.
The exhaust valve under the frame could be used either to just exhaust the tag with the lower SV closed, or exhaust both with the lower SV valve open, as it would be in the travel & raise position.

I believe the lower valve in your picture is an ABS Modulation Valve.

That would answer my question as to why line pressure is introduced into the rear leveling further down from all controls.

Let me know what you think

Thanks again