Need advice on installing new fuel line

Scott's dead right. The 5/16 line is big enough for what you have. BUT it's not a bad idea to upgrade. I guess you have a mechanical pump? That right there is the problem. It's easier for a pump to push the fuel up the hose against the car's inertia than to pull it. A properly chosen and mounted electric pump will solve your problem. If you do decide to upgrade to 3/8 line, it will be plum stupid if you continue to use the 5/16 sender. Only X amount of fuel will flow through that 5/16 hole and that ain't gonna change. Just cause it has 3/8 line in front of it means nothin cause it still has to flow through a 5/16 bottleneck. A stainless 3/8 sender ain't but 50 bucks. You can get pre bent 3/8 line for about 79 bucks. really a cheap upgrade. I'm even goin with 3/8 line on my slant six, just because. Of course...also as Scott pointed out, you need to make SURE your problem is fuel first. Last thing you wanna do is end up droppin money with no change. What "I" would do in your shoes if I determined it was a fuel problem would be this: Ditch the 5/16 line for 3/8.....just because. Add a GOOD quality (Holley Blue pump comes to mind) electric pump. Mount it as close to the tank as possible. Run an inline regulator with a GOOD quality filter AND include a fuel return line. This will keep cool fuel recirculating constantly through the carb. Will cut way down on hot fuel problems. Oh...and is this car driven on the street at all? If so, you WILL notice a big difference in fuel economy with the vacuum advance disconnected, and I garrantee you would see a difference on the time clock. If it's drag only, then ditch it.