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
