Fuel gauge and sender compatibility.

No aftermarket sender will work correctly with the OEM guage.

You lost me a bit with your question. My confusion is are all of the measurements based on OEM and spectra sender and aftermarket guage?

Keep in mind the tank itself is not retangular. It has the cut out for the spare. What I'm trying to point out is that the 1st 5 gallons or so will lower the float faster then the following 13 gallons.

Did your aftermarket guage recommend a sender or a ohm range?

Do you still have your OEM sender. They can be referbushed.

OR I will buy it from you for a reasonable price.