fuel sending unit

The new ones aren't calibrated correctly. In fact, if you compare it side by side with the original A-body sender, it pivots at a different point, has a different length and shape arm, and a different scale. So it's no surprise it doesn't read the same. I gave up on the new ones and found an old one where someone had upgraded to a larger fuel line (3/8 instead of 5/16) and was willing to let a good sender go. I'd recommend you try to do the same.