Hay!!!!!!!!!! I think I figured out why the sending units are different.......because there's a return line on the fuel pump on all cars with an A/C, there's also a return line on the sending unit.........
((((Eagle's theory is the return vent line is needed because of higher idle speeds when the A/C is running.)))
So an A/C car has two lines on the sending unit..............
And a non A/C car has one line on the sending unit...........
OK,,,,,,,,,That's all making sense to me now........................ Later...........