Better to be too large and run it through a fuel pressure regulator than too small and run lean on the motor. Maybe more plumbing, but a return line to the tank may be in order as well.
ON My BLOWN MOTORS WE RUN FROM AS SMALL AS 12 TO AS LARGE AS 16 TO THE FUEL PUMPS. Then run loop lines from the reg back to in front of the pump or to the tank with min 8 lines. Make sure the orfice in the regulator is large enough so as to not induce cavation in the return lines.