Venting

So first off, your vent line is 5/16", not 1/4". Mopar didn't switch to 1/4" vent line until 1972.
Assuming you have a stock tank and fuel setup your best bet is to leave it vented to atmosphere. Put a small filter at the end to keep crap from getting into it. It's so far from the fuel tank that you won't have any insane vapor/gas smell issues. Don't worry about it.

I wouldn't rig it to be a fuel return line unless you had a '72+ setup.