[Dave at Pelican Parts]

EGR was added in 1975 in California (and I think Massachusetts?) cars.

It sounds like the "bypass relief valve" that Jess is referring to is the valve in the fuel pump. If the pump develops too much pressure for even the fuel pressure regulator to handle, that valve will open and pressurized fuel will be diverted to the "R" port on the pump, joining with the return from the fuel pressure regulator and going back to the tank.

--DD