I have a 1969 Cutlass Supreme convertible with a 455 big block. I need to replace the fuel sender but I don’t know which on to use.

 

0-90 ohm. Why does it need replaced? Have you verified it bad or just throwing parts at it?
most common problems are the tank ground or a connection on either end of the front to back ribbon cable.
You should be able to ground the sender wire and make the gauge drop.

 

If your question is about single vs two lines, does your car have fuel return or not? How many lines go in and out of the fuel pump?