Tubing is measured by OD, so you have 5/16" steel line. It should be available in various lengths at any parts store, with male inverted flare fittings installed on both ends. Use male pipe thread to female inverted flare adapters at the tank and the fuel pump to adapt the line to the existing plumbing. If you have to cut and flare the line to accommodate an oddball length, be sure to do a double flare- - - -steel lines crack if you attempt a simple single flare on them.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!