if your running a return to the tank you always put it after the carb. you want to hold the set fuel pressure in the float bowls. that way the carb takes what it needs and the rest goes back to the tank.
Unless you use a real "bypass" regulator, which IMHO is a better system. Then it does not matter, just mount it close to the carb. Inner fender worked for me. Please reference these installation instructions for the bypass regulator: [ame="http://aeromotiveinc.com/wp-content/uploads/2015/04/133-0111-0revF.pdf"]http://aeromotiveinc.com/wp-content/uploads/2015/04/133-0111-0revF.pdf[/ame]