My 78 Malibu with a 305 has a 3/8 feed. All of the EFI turbo Buicks also had 3/8" feed lines.
From my own experience, the 5/16" feed lines will not be a restriction unless you are supercharged and well over 500 horsepower to the tires.
From my own experience, the 5/16" feed lines will not be a restriction unless you are supercharged and well over 500 horsepower to the tires.