EFI return line, use emissions return?

I'd use it. Might not be as big as the system "wants" but it's a heck of a lot better than a recirculating situation.

So far as TIG welding in an additional fitting, you don't necessarily need to TIG it. I actually added a 1/4 return line for my 67, which had none, for a vapor return system. I simply took the CO2 regulator output from my MIG, and filled the tank with CO2, then oxy/ acetylene gas brazed (hi temp silver braze) a 1/4 line into the tank. I believe you can also buy repop tank senders with a return line in them.

What year is your vehicle?

Here's a shot out of the 72 shop manual, which you can download here:

http://www.forabodiesonly.com/mopar/showthread.php?t=132309&highlight=manual,+download

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