I'm think I'm throwing in the towel

[CT_V-20]

Structural work sure intimidates me, but there are others here that seem to take it in stride. For sure if you don't have the time and it costs too much, it ain't gonna happen.

I wonder if the plumbing down in the cuddy is from a previously plumbed head. With the below the water line fittings you described, combined with the age of the hull, it's possible the head was simply plumbed out the bottom through the big hose and the smaller hose was a vent. Just a guess.