OK, ,more progress on the 6.3. The fuel is being replace and this pic shows why. Many years ago someone has crushed it by lifting the car incorrectly with a hoist ,jack or….forklift. In fact it was squashed in many places.
next pic shows one of the other crush points.
As can be seen in the pic,the pump was mounted solidly and is 150mm too high,meaning that once the fuel level drops to 1/3rd tank level the pump was starting to starve for fuel . These pumps are not a suction pump,but a pressure pump.