So, I'm in the process of stringing my tubing back onto the freshly restored frame and was pondering the same thing. The return line goes to the canister by the battery then where? Since there was an aftermarket Holley on the engine when I got it, this wasn't hooked up. I assume it's related to emissions.
Does it have the potential to help mileage if hooked up to where ever it goes?
Also, is the factory tubing stainless? I polished the gasline/brake tubing and was wondering if it would rust unless I coat it. Is clear laquer effective for this or is there a more professional method?