I wouldn't rely too terribly much on photos of original cars as it appears that no two were alike. The brake piping for my left hand steering S4 was set up at the factory for a right hand steering car. All of the piping for the tandem set up went from the four wheels to the right side of the engine compartment, just below the carbs. Then, they were connected to two more pipes that ran in front of the engine, over the vacumn tank to the left hand side where the MC is. So there were actually three lines on top of the vacumn tank (front frame cross member). This made for a nightmare when trying to determine the sequence for bleeding the brakes as the furthest wheel from the MC was actually the rear left and the closest was the front right. I rerouted the entire system removing over 13 feet of brake line and now I can bleed the brakes using half the fluid I used to use. As far as running the pipe to the rear, originally, it went under the right side of the frame secured by the clips that Tom referred to. I rerouted it away from the road high up in the frame on the left side. There are holes provided in the bulkheads and I added grommets.
The plastic fuel line, which ran low in the frame on the right side was replaced by metal brake line that now runs high within the frame on the right side through holes that are provided in the bulkheads just opposite the brake line. I think I used the longest piece of metal brake pipe I could find (8 feet) and it reached from the tank to a foot or so from the mechanical pump. I then switched to rubber fuel line to compensate for engine movement. I really don't see the need to go to expensive braided fuel hose as I don't expect the metal brake line mounted high in the frame to fail.
I would up with a neat installation having both lines (fuel and brake) mounted away from the road, high up inside the backbone on either side. One word of caution. I'm not sure, but because the fuel line is mounted much higher than it was previously, I think the fuel has a tendency to drain back into the tank when the car sits. I may modify this by putting a trap in simplying using a longer piece of rubber fuel line at the front between the pump and the end of the metal fuel line and looping it down just like the trap under your kitchen sink. That should prevent the fuel from draining back to the tank.
Good luck,
Frank Howard
'71 S4 SE
Minnesota