jb...My boat (#511) and Neil's boat (#600) are of similar vintage..both '77. I can't recall if you had posted previously what hull # yours is.
The two galley drawers to port of the stairs are easy to remove...the frame generally has 4 sheet metal screws into fiberglass..also easy..this gives you enough access to stick your head and a big light in there. Have you tried that yet?
Based on Neil's description, I would guess Catalina made these "harnesses" in 6'-8' lengths..as they went to longer runs, they just added another length(s) of harness..I had two short runs (at the engine and gauge pod) with a 6'-8' run in the middle..add a wheel and an aft gauge pod and it could be two or more sections..
Just throwing it out there for things to look at...I have no positive data on this.