I would suggest wiring up the sending unit to the fuel gauge and a good ground (to the sending unit bolt flange) before installing the unit to make sure that the gauge goes from empty to full as you move the float arm up and down. This will allow you to make sure that your problem is actually the sending unit rather than the gauge. Also as you insert the sending unit in the tank, make sure the float doesn't contact the side of the tank, and bend the arm if necessary to prevent the contact.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission