Some cars came with what is sometimes called a vapor return line, which goes back to the tank. Some cars did not come with a vapor return line.
Some pumps have a fitting for the vapor return line & some don't. If you have one that does, but don't need it, than all you have to do is make a good plug for it. I did this on most all my bracket cars. If I remember correctly I used a short piece of fuel line hose, a bolt, & 2 hose clamps. Worked just fine.
Obviously, you don't want the plug(or any gas line fitting) to leak gas. I've found that the small, narrow worm gear clamps can cut into the rubber fuel line and, over time, cause a leak. So, years ago, I began using clamps with wider bands, of at least 1/2". I recently bought some clamps at O'Reilly which have a 9/16" wide band. But they ain't cheap, @ $1.29 each.
For those who might wanna find some cheaper clamps, with 1/2" wide bands, i found some online at Grainger, Amazon, & Wal Mart. Haven't ordered any yet. You can order from Grainger online, then pick 'em up at your local Grainger store.
OR, some of you guys might be able to find cheap wide band clamps at your local parts store. I have no idea. For good prices on most stuff, I have to buy online.
Back in the old days, if I didn't have any wide band clamps on hand, I'd use 2 of the narrow band clamps, butted up together. The wider band width seems to seal the hose connections better, with less chance of cutting the hose. Another upgrade is to use fuel injection grade hose. It has more reinforcing fibers than the old type regular low pressure hose.
Then there are those who will plumb everything with AN fittings & metal braid covered hose. Can't speak to that. No experience.
Some like to use a return line in order to keep the gas a little cooler, by keeping it circulating, rather than having it stay in the pump longer.