Here's what I know. Bought a '73 brand new in July '73. It had mechanical pump only, no electric pump. Later that summer I took it in complaining of vapor locking. The dealer wrapped the fuel rails around the valve cover with a reflective metalized wrap. Took it back later, still vapor locking, but not as bad. The dealer installed an electric pump back at the tank. To be honest, the vapor locking was never completely cured in heavy summer traffic for the 20+ years I drove the car.
I now have a early '71, manufactured December '70, I'm the 2nd owner. I believe it's a series 1 car based on things like body vents on hatch, position of ash tray, rear window defroster line direction, etc.. It has the green / black wires for a fuel pump hanging down back at the tank. Haven't hunted yet but I presume the other end to be in front of the fuse box in the front left of the console area. I plan on converting to electric fuel pump in the next month, so I'll be digging into the console to find the wires to jumper with an inertia switch to activate the wires back at the tank. Under the fuel gauge sending unit on the tank are a couple of pre-drilled tabs that I'm guessing are for mounting an electric fuel pump. Based on my car I'm betting that the Z's were plumbed from the git-go for electric fuel pumps.
Side note: Found a blue taped wire w/bullet connector coming out of the harness right under the battery that is hot when the ignition switch is in the engine running position. How did Datsun know I needed that right there for my electric fan controller?