Greg,
that much discrepancy in the gauge reading vs what's in the tank is more than just the float being a little out of calibration. When we were discussing this some time ago & I made an alteration to my float position it was only off by a little less than a quarter of a tank. That's not much movement on the float arm. I don't think that an NOS piece will cause you issues, it's a pretty simple device, if it's a domestic piece I'd lean to that before an asian offshore item.