Fuel sending unit calibration

Most aftermarket sending units are wound with a linear resister. Since our A body's have the spare tire recess in the upper portion of the tank, the factory used a non- linear resister on the sending units. No amount of bending the arm will ever get the gauge to read properly. Either a electric/computer device to compensate or a aftermarket company coming up with the proper non-linear sending unit. even if some one come up with the proper resister and we installing it on our older sending units would be nice.