65 Cuda Gas Tank Vapor return line

I don't think you understand. The tube in the diagram above is the VENT It MUST be to open air, or the tank will either have internal pressure or a vacuum, depending on temp, etc.

All these cars had that type of vent until 70 for some cars and 71 for all cars when the "carbon can" system was implimented

What the second tube is useful for is a "vapor return" system, using such as Wix 33040 --5/16-- or 33041 --3/8-- fuel filters. These filters have a 1/4" fitting which has an orifice, which you install so the 1/4 fitting is at the top (air/ vapor bubble.) You run a 1/4" (or larger) return line from there back to the second fitting on the sender and it constantly "fights" vapor lock

The emissions control / carbon can system in later cars is a completely separate deal. It replaces the simple vent system (open) and vents all vapors into the carbon can, where they (it says here) are periodically flushed back into the engine.

Here:

http://www.forabodiesonly.com/mopar/showthread.php?t=183956