Hello I will help you with your question,
The eccentric is the lobe on the cam shaft that pumps the lever on the fuel pump to move it and pump the fuel.
All you have to do is remove the old pump, clean the mating surface and install the new pump making sure the lever is under not on top of the cam shaft then tighten the pump into place.
Transfer the lines to the new pump on the same fittings and you are done. Remember that with a mechanical pump you are pulling fuel from the tank so the line to the tank has to be air tight or you are only pumping air.
Let me know how I can help you with this
NO, all you need to do is pinch the line off to keep the tank from draining or work quickly. Open the cap to release pressure and then seal a plastic bag in the cap to seal the tank neck and the fuel should stop.
I use brake hose clamps ($5 for two) or a pair of needlenose vise grips with the jaws padded with vacuum hose to pinch the line, it does not have to be pinched tightly just enough to keep it closed.
Let me know how i can help