I know some people like to keep the mechanical pump for various reasons, like looks and originality, etc... and they work well...
But I'll throw in my $.20 in favor of electric fuel pumps. I lived in Florida before, and if I parked the car for a few days or a week, the fuel would evaporate from the carb and it would take very long to start the car, because the engine had to turn over to run the pump and bring fuel to the carb. This puts an unnecessary strain on the battery. If you also drove mainly short distances, the battery would not get charged back up, necessarily.
Another option is to use both. I am plumbing for an auxiliary electric 'inline' pump controlled by a switch on the dash:
The pic is an Airtex.
This is perfect for the scenario that 70Nova paints. The car has been sitting = the carburetor bowl(s) is/are dry . . . just flick the switch and prime the system. Start it up and drive away on the mechanical pump.
Best of both worlds.
Should the mechanical pump fail one could use the electric pump as a backup - but you would likely need to plumb around the failed diaphragm - otherwise the electric pump would push fuel into the crankcase.
