I'm not sure if this helps but in 1984 the Camaro with a 305 H.O. engine had this exact same setup. The electric fuel pump in the tank served to both prime the fuel system and prevent vapor lock. It also had a mechanical fuel pump and a return line. I think that the pump would just run to pressurize the mechanical fuel pump and all excess fuel was returned to the tank. The mechanical fuel pump just used what was needed to feed the carb. This is a neat setup. I'm not sure if it would work for our second gens but I have considered trying it on my 71 since it has the Z28 fuel system with a mechanical pump and return line.
Roadkill garage used a Bosch electric fuel pump on a EFI system. They said that it is useable on a carburetor with a regulator. I'm going to put one on my 87 S10 drag truck with a return regulator which dumps off the excessive fuel pressure and keeps it below 7 psi from idle to WFO throttle.
No matter which type electric fuel pump --- suggest wiring it with an Inertia Shut Off Switch as are OE in every production vehicle w/ OE electric pump. Inertia switches available as new OE replacement for under $25.
Very simple to wire in and can be reset with a simple push button. Think of a wreck where fuel lines are compromised and pump keeps running --- ugly. That's why inertia switches are OE.