Reply to "heater questions"

The valve disassembles further, and below the lever is a shaft. The o-ring encircles the shaft. Its been 15 yrs since I took mine apart- can't remember the exact moves to do this but it wasn't difficult.
The steel water tubes run inside the console & above the floor so doing as you propose will require drilling two holes in the floor to run new tubes up from the water pipe area. By removing the whole console upholstering and the drivers seat, you can get to the old tubes. I suspect the engine would also have to come out to insert new tubes, as they're about 4 ft long. I've never heard of the heater tubes failing in use; what normally fails is the short hoses from tubes to/from heater valve. One guy did have a stock pipe fail, when a console retaining screw was drilled into the pipe at the factory. Instead of replacing it, he welded the defect in place as changing the tube was too much trouble. He was a Ford dealer mechanic......