Fuel line size
 

Finally ran the new fuel line on my 49 F-1. I have installed the mustang tank in the rear under the frame rails. I am running a SBF and used 5/16 fuel line. When I finally installed the rubber fuel line onto the pump at the motor I noticed it was 3/8. My question is does anyone see any reason I should re-do the line in 3/8. What did you guys do? I think it will be fine but thought I would ask your opinions.:-huh Thanks

I always defer to OEM since that is where the money is spent on development. What did the 70 mustang use? GM normally used 5/16" for lower HP engines and 3/8" for the higher HP engines. For example a 200HP engine would get the 5/16" but the 250HP would get the 3/8"..but then it depends on how you plan on using the truck. A higher HP engine putting around doesnt need much fuel.
I converted lower HP cars to 396CI/325+HP engines with the original 5/16" fuel line and ran to 6000RPM with no issues, so it will depend on how much fuel your particular engine needs and how you run it.

5/16" will be just fine . :-X22