Will,

If your 79 is like my 84, that line is only about 18" long. It goes thru a opening in the frame to a brass fitting and attaches to a metal return line headed toward the front of the car. You reach it by jacking the rear up, and its just in front of the axle. Just seperate the line at the fitting to remove the sending unit, spray the fitting with some sort of penetrating oil because they are often troublesome to remove. If by chance you can't seperate the fitting or you damage or twist the metal line, simply cut the metal line with a tubing cutter, cut the old plastic/rubber line off the sending unit, and replace with 5/16 rubber fuel injection line and two hose clamps.

Good luck,
--
Bruce S. near D.C.