I repaired a similar fitting on a 300D turbo radiator with a two piece valve stem used for custom wheels. This valve stem goes through the valve stem hole and then a nut is screwed onto the stem to hold it in place.
You can get such a valve stem at your local custom wheel dealer. To put it in place, grind the area flat where it will seal. Push a wire from the outside of the hole through to the neck or large hose connection. Slip the valve stem over the wire and bend the wire to keep it from coming off. Then pull the wire with stem attached to get the stem through the hole from the inside. Slide your nut over the wire and tighten. Don't forget the rubber washer seals.
Remove the valve core from the valve stem and clamp your hose in place. Worked great for me and saved buying a radiator.