It sounds as if you have checked everything, but according to my schematics the 57 CVR was not grounded. You have a CVR for the 60-66 Thunderbirds and I don't think it would be the same for your 57. There should be a black wire with a green band coming from the A terminal of the ignition and black with green band wire going to each of the gauges. I would remove the ground wire that you have attached and see if everything works as it should. In 57, I believe that the temp. gauge will fall to the hot side and the fuel will fall to the empty side when the key is off.
Fort Wayne, IN