I recalibrated one some years ago via resistors, wired them in series at the fuel tank with the sender wire. Had to keep adding resistors in a parallel bundle until I got the right amount (lots of crawling under the car with resistors and then out to check the gauge!). After hitting the right combination I sealed it all with heat shrink. This was for installing a used OEM sender so it's not the same situation.

As I recall it was off by 1/8 tank at one end of the gauge but was close enough for me. It either read E at a true 1/8 tank or never reached full.

I recently installed a new Spectra Premium sender in another car and it's off by 1/4 tank. I think this one needs the float arm rebent. I'll empty the tank, fill it with 6 gallons (24 gallon tank) and see what adjustment needs made to put the gauge to 1/4 tank. 6 gals should be below the gasket of the sender and permit me to R&R teh sender without spilling fuel. Can then maybe hold the float to the top of the tank somehow and see how the gauge looks for full.