This quote from RansomeT's post: "Only issues I have seen after many years is that where I branched off to feed the to engine banks with a deadhead, it has a tendency to vapor lock after setting 10 minutes or so with a non running warm engine. Takes about 15 minutes to cool off and start. And the fact that the SHO is too fast for my safety equipment. " is exactly why you should always mount the fuel regulation valve down stream of the fuel rails. The fuel regulation valve maintains the set fuel pressure by bleeding off excess fuel so that the set pressure is maintained and the fuel that is bleed off is returned to the tank. By mounting this "relief valve" down stream of the fuel rails, i.e. between the fuel rails and the fuel tank, the fuel that is bleed off insures a constant flow of the fuel, at the set pressure, thorough the fuel rails. Most of these valves are of a three port design which makes it appear that you should run the fuel line from the pump into the through port and then connect the return port to the tank line. This method fits with the mounting of the regulator before the fuel rails but when you do this you have fuel dead headed at the ends of the fuel rail, and on start up after a long time of non operation you will have entrapped air at the very end of the fuel rails which takes time to be dissolved into the fuel and you will have problems with heat as the fuel that is dead headed at the end of the fuel rails can pick up heat and boil as described by RansomeT. If you uses the fuel pressure regulator at out let of the fuel rails then you need to plug one of the through ports and then only run the return line back to the tank.
Regarding referencing the fuel regulator valve to the boost pressure it can depend upon your ECU, some of the very latest designs do monitor the manifold pressure with a transducer and then regulate fuel pressure based upon this, but to have this type of system you need to have a fuel pump that can vary its speed, output, to control fuel pressure, this is not the system you are describing. The standard electronic injector is a rapidly opening and closing valve that is designed to pass a certain amount of fuel based upon the differential pressure between the fuel pressure and the manifold pressure. The amount of fuel is regulated by the amount of time that the injector is held open and, of course the differential pressure that it is subjected to. Therefore you need to reference the fuel pressure regulator to the intake manifold pressure which will compensate for the intake manifold pressure being more or less than atmospheric pressure. All good regulators will have typically a 1/8 NPT connection in the diaphragm chamber which is the port to connect the manifold pressure to. This line should not be larger than 1/4 inch max. I am not aware of any after market ECUs that will monitor manifold pressure and fuel pressure and then modify the injector timing pulse to maintain the required fuel flow based upon a varying differential pressure but I am sure it could be and might be done.
Rex