Grounding stock gas tank ideas? No metal fuel line...

Take one of these, MF290 - 1962-76 Dodge, Plymouth; Fuel Sending Unit Ground Strap; 3-3/4 clip one end off, solder an appropriately sized ground wire on it, put an eyelet on the other end. Clip the remaining clip to the supply line coming out of the sender and screw the eyelet end to a good, clean ground.