I do not know what you are speaking of when you talk of a metal part and the plug.
But it sounds like the coil has failed -- Have you ever replaced it -- they tend to just go like this.
If you are not getting ANY spark on ANY plug and all else fails to show up -- thats what I would think.
normally you would still get something with a crack in the cap - they are quite robust in that motor. I can not remember what the cap and rotor cost for the 560 - but I remember them being pricey for what they are. The wires tend to go but not all 8 at once
I do not remember what the coil cost is but they are very simple and are not usually that $$.
before I spent a lot tto tow the car and then pay to scope it I would look to the coil.
You should more than likely smell gas as all is actually working except for the creation of the spark - this would rule out a fuel problem -- also do you hear the pump cycle.