OK, I've been learned a little bit today... I think I understand the fuel system much better now. Looks like its a mechanical returnless system. Also looks like the filter has a built in return line to keep the pump flowing and cool since it provides much more fuel than is actually being used by the engine. The fuel rail has the snap ring style mounted "damper" that looks exactly like a pressure regulator, but it isn't actually controlling the fuel pressure. The fuel pressure should be controlled by a regulator that is mounted inside the fuel tank, in the pump/sending unit assembly.
If all this is a fact, then it's going to be a little more tricky to control the fuel pressure under boost. I'll have to modify the fuel system more than expected. I found a nice article on modifying the internal tank regulator to force it to go full pressure, swap pumps with the high flow unit, and then use an external regulator. Massapi makes an external regulator that uses manifold pressure to control it under vacuum and boost. I would run a vacuum hose to the regulator, and mount it next to the stock fuel filter location. I'll replace the filter with one that doesn't use a return hose. Then I'll use the old return hose that was on the stock filter, and connect that to the regulator.
The stock fuel filter has 3 hoses. One in, one out to engine, and one return to the fuel tank. When the engine isn't using much fuel, then the excess fuel needs to go somewhere, and the filter's built in return line lets it go right back to the tank. In my scenario, I'll let the regulator decide when and how much gets returned to the fuel tank.
As for mounting it under the truck, I'd much rather run a vacuum/boost sense hose from the engine to the rear mounted regulator than to run another fuel hose all the way to the front of the truck. It's easier and safer to have less fuel lines than necessary.
