SS Slant Six Dart

the line is overkill and will lose psi at the previous psi pumped, but you have a new higher psi pump it sounds like, so...

fwiw
I use 5/16 fuel line with 410 inches, which fed it fine over 6500 rpm.
Built 440 rev'n 6800=5/16 I built the motor for 68 dart
340 4spd hitting 7200 rpm=5/16 fuel line

Ill add all used stock fuel pumps too.

put your money where it will make + difference/power.jmo