I know this is an old thread, but I’m doing the fuel tank and fill hose on my 263 Chase as well.
I have a plastic perk fill “fitting” with a metal screw cap. Like the OP, the screw that holds the metal screw cap to the plastic fill fitting has a ground wire on the bottom. The wiring goes into the factory harness and is labeled “fuel grnd”. This is a factory design.
Question..leave as is, or ground fitting to tank? Tank will be grounded to battery neg regardless.
I am not sure what you are describing about the metal cap has a screw that attaches it to the fitting.
If there is a screw on the cap it self, that is for a retaining chain to keep the cap from getting accidentally lost.
The purpose of the ground wire on the fill to tank run is purely to discharge static electricity. If static electricity builds, there is a greater possibility that when inserting or removing the fuel nozzle, a spark could be generated.
That circuit for lack of a better word is not the same as a wire out of the harness that is labelled fuel ground. That is the negative connection for the sender. If you had a plastic tank for example, you would need that connection in addition to the sender 'signal' wire for the sender to work. Typically the ground tab of the sender is connected to a common point on the gas tank and that common point is connected to the battery ground circuit.
If you original tank setup had a ground wire connected to the underside of the fuel fill fitting and you are using the same fuel fitting, there should a connection the ground. If the fuel fitting is plastic, regardless of the cap material, you do not need a ground at the fitting. If you have a metal gas tank, it should be grounded.