I use mechanical pumps with no electric helpers on every vehicle I own. Even if they sit for long periods of time, it isn't difficult for the mechanical pump to get enough gas up to the carburetor.
The good thing about your 51 is the gas is all gravity fed to the pump so it doesn't even have to do any work to get the gas from the tank. It just flows out of the tank to the pump naturally. If the pump can't get enough gas up to the carburetor to start the truck, it probably needs to be rebuilt
