What size fuel line is absolutely required?

to big of a line and the pump have a harder job for pushing the gaz
under hard acceleration , like I said you should decide on what ever
pump you wanna run with the built your making there and run the line
the pump builder he is sugesting you

I ran the same pump for the last 12 years ( holley black pump )
for a 410 cu.in. with nitrous with a #10 line and 2 regulator
one for the carbs and the other for the nitrous setup
did great but NOW IM GETTING OLD

and i wanna change the pump for one that make lest noise
and the way I see it I will need to change everything as gaz line
because about every company will suggest diferent size of line
even for the return line so ... contact the manufacturer of the pump
your choosing or you have and ask them advice

they built there pump so they should give you the correct size of line you need