I'm sorry, I meant the specific combination of 5/16 feed and 1/4 return line is a no go. That would overheat and kill the fuel pump very quickly.

Here's a helpful article where Aeromotive recommends certain line sizes for different horsepower engines.

http://www.stangtv.com/features/fuel-system-troubleshooting-killing-gremlins-with-aeromotive/