Chuck, I had a similar issue with a new sending unit on my '57. Full only showed about 3/4. I never tested empty by running out of gas, so perhaps my issue was different.
The solution for me was to do exactly as you suggest...bending the float arm down. A full tank was not allowing it to reach its full swing. I did it in small increments and tested in between with a completely full tank. I have a battery disconnect switch and I turned off the battery in between tests for safety. I stopped when the needle showed the entire full dot. It now works fine. I have not run it down completely to empty, but I have run it down to where I had two gallons left based on how much it took to fill. It seems very accurate.
Matt
Thanks for confirming that solution Matt. I haven't tried to correct it yet since I am concerned the arm may not drop far enough to accurately measure empty. It's encouraging to hear it worked okay for you.
