Very few fuel pumps had a return line. No return at the pump no return at the tank. The only A/C Delco factory return line mechanical fuel pump I am familiar with was the 325 horse 396 that had return line when fitted with a Rochester QuadraJet carburetor. It supplied the carb with all the gas it could use and what it couldn't use was returned to the tank under reduced pressure from the pump via a second steel fuel line.
A mechanical pump is fixed in it's pressure by the spring inside the pump. It is the spring inside the pump and not the lever arm that pressurizes the fuel. The spring arm only sucks in the fuel as it moves. The spring above the diaphragm pushes the fuel out and up to the carb.
Since the spring never applies more pressure than the carb needle and seat can handle there is no need for a return line.
With electric pumps located next to and under the gas tank or fuel cell the pump pressurizes the fuel from 14 to 87 psi to push it forward and for it's use at that pressure with EFI if needed. Since a carburetor can not handle that kind of fuel pressure a return line is required. The return line returns all unused fuel to the tank at a high pressure and has to be segregated from the pick-up to keep the fuel from foaming.
In cars made before 1973 when cats and charcoal filters for gas tanks came on line there were only two lines in the pick-up the actual fuel line and the gas tank vent. This added a third line to the pick-up, but it wasn't a return line just a second vent for the gas tank (one allowed filling the tank, without it backing up, and the second line went foreword to the charcoal filter to hold all of the gas fumes until you started up the car. The added gas fumes helped the overlean smog era carbs to crank up and do nothing to impede performance so they shouldn't be removed (nor should you disable the PCV system, as it helps rather than hurts performance).
The rest of the junk that I rip off (spark control, thermostatic choke for hot air into the carb, etc all hits the trash bin when I had a car so equipped before I dropped in a real non-Smog era motor (which have lower compression, lean jetted carbs, and retarded timing distributors to pass the sniff test should they have been installed in your sixties era car as a replacement).