I just converted my Goddaughter's '70 Duster 360 to EFI. It had the original gas tank with the 4 vent tubes on the side going into the vertical vapor separator in the trunk. We replaced it with an EFI ready tank with one vent tube coming out of the top center. The fuel pump also has a vent which is tee'd to the tank vent just forward of the tank.

The original metal vent tube running up to the engine compartment was in pretty sad shape, so I decided to run a single hose from the tank to the rear tube of the separator, cap the other 3, and run a short piece of hose with a cheap fuel filter on the end to keep bugs and crud out as the vent.

The nipple on the tank is 5/16". 2 of the 4 tubes on the separator are 3/8" and the other 2 are 1/4". I had to make a coupler to go from 5/16 to 3/8".

I'm thinking this sort of mimics the pre '70 setup where a tube runs from the top of the fill pipe straight down thru the rubber floor gasket and vents into the atmosphere.

Any thoughts? Good? Bad? And above all, safe?

I would think that would be fine assuming you're able to blow through those lines on the evac tube without restriction. Mine on my Barracuda were blocked with dirt, rust, and 40yr old spider skeletons. With a return line setup, I'd imagine that vent tube only has to deal with minimal pressure changes mostly due to fluid expansion. I'm far from an expert on the matter though..

Can'ttell from your pic, but you normally want the vent as far above the tank as possible to prevent leaks when filling. IE: Hot summer day you fill up with gas that is a lot cooler from being stored in underground tanks. As it warms up it can expand and will overflow through the vent line as it has nowhere else to go.
Might check out Tanks inc. website
TANKS INC>