If your engine is rubber mounted, and it is, and your fuel line is mounted to the frame,and I suspect it is, then a flexible connection is required. If that isn't there then at the most unhandy time you are going to end up with a fuel leak. The same if your fuel tank is in the cab, a flexible needs to be involved. Another advantage the the rubber line is that the fuel line won't be used as a ground for the battery.
