I would suggest a 3/8" min supply and the same for
the return.. if your going with EFI it will need a
good return.. I myself run a 1/2" supply and return
with my set up.. it was carbed but now I run a Holley
multi point EFI and the system is good up to 700 hp..
if I were to go more than that I would need a bigger
pump and injectors.. the rest will work... the issue
with a 3/8 line that I dont like is the bends.. if
you get any kink at all it reduces the flow... the
ID is already 5/16" on a 3/8"
EDIT
Also... if you keep the stock tank I would add a sump
to it... injection doesnt like to have air sucked
in and if you run low in the tank it will suck air
in