What about the special clamp for the piece of fuel line between the sending unit and the fuel line the rubber connects to? The sender grounds though THAT FUEL LINE, so the clamp provides the circuit between the sender and the fuel line. If gone, that clamp might be replicated with a piece of wire or similar between the sender and the fuel line, possibly.
About the only time the C-body senders/gauges were really accurate was at "F", "middle", and maybe "1/4 left". Not uncommon for exact accuracy to be off a gallon or two here and there. A-bodies were noted for running out of gas at the 1/8th left area on the gauge.
Not hard to figure out your specific vehicle. When it gets to 1/4 left, put an amount equal to 1/2 tank in and see where the needle goes. When it gets to 1/2 tank, fill it up to where the nozzle clicks off, then note how much more when the next nozzle click happens. Let that be "total full", rather than "stick your finger in it in the filler neck" full.
Chrysler rated the non-wagon tanks at 25 gallons, but the replacement vendors say 23 gallons. Whatever works for your car.
CBODY67