My 2002 LS1 engine needs no return line coming from the engine compartment. All it needs is one 3/8 inch diameter fuel line from the tank to the engine.
However, outside the tank, and somwhere near where you mount the tank, you'll need to plumb in a fuel regulator. So you have 2 lines coming from the tank to the regulator (supply and return), and then the one supply line going forward from the regulator to the engine bay.
My setup involves using an aftermarket made tank with an "in tank pump". It's 16 gallons I think. I wish I could have found a larger one, but didnt' want to spend the money for a custom made tank.
You can also go with a tank that uses an external pump, but guys have found those to burn up quickly, AND when there's no baffles inside the tank, you end up with fuel starvation issues when cornering with less than 1/4 tank of fuel.
So look for a tank that has internal baffles, in-tank pump, and fits between your framerails and you're good to go with a later LS engine.
Here's how I did mine...
Attachment 2169
And I fabricated a bolt-in tank mount to center the tank between the frame rails, and position it up high (since a wagon has alot of space below the floor).
Attachment 2170