Sorry, I don't understand the concern about a check valve.
The fuel in the carburetor CANNOT possibly backfeed to the pump (unless you guys are parking the trucks upside down - hard on the paint on the top of the cab
)! The fuel inlet in the carburetor is located ABOVE the fuel level in the carburetor; and there is no direct connection for a syphoning action.
It might be possible that the fuel in the fuel line would backfeed through the pump back to the tank if the pump inlet check valve is bad; but if the fuel was not evaporating out of the carburetor, the carburetor bowl would contain sufficient fuel to start the engine, and run it until the fuel pump regained its prime.
Check out the Reid Vapor Pressure that efi will withstand (modern fuel) then check out optimal Reid Vapor Pressure for a carburetor.
Jon
