Porsche added a small restrictor in the return fuel line for 1973, apparently:
My fuel pressure is on the low side of the .8- 1.0 bar spec required, so I might add a bit of restriction at the tank return. Pinching the return line gives a pretty good idea of how that will work, and I should be able to dial it in to where I want it, about 15psi. That will have to wait until everything is assembled in the car.