You can use a meter match to correct the gauge readings with the replacement sender that does not read correct.
I just calibrated one today and documented the readings. Basically I drained the tank and read the sending unit. 74.3Ω empty. The meter match has four calibration points so I used empty, 6 gal 10 gal and full. 6gal (3/8) is 41.1Ω. 10 gal (5/8) is 21.7Ω and full was 9.9Ω. These are readings directly off the replacement sender with the exact mount noted in the tank.
Are you working with an OEM sender or a replacement? You will never get a replacement one to read correctly through the whole range simply by adding a resistor due to the shape of the tank. The new senders do not account for the odd shaped tank.
Someone could make a small fortune if they made a correct sending unit for mopars that actually worked.
