You need to deal with venting the tank, which was done by the 1/4 line running up front to the canister system. The cap was a "pressure vacuum" thing which acted sort of like a "pop off" valve, IE so much either vacuum or postive pressure in the tank, and the cap would relieve.
The thing is it is VERY advantageous for preventing vapor lock to use the 14" line as a vapor return line, so in that case you need to "get back there" and rework the line connections a little from the tank to the vapor separator.
Here's the thing about that "can back there." At least some of the lines are not in the bottom of the tank, and at least one IS. That line, or one or two others, DRAINS any liquid in the separator.
You need to keep that in mind.
Yet another way would be to set it up just like the pre --carbon can cars---a vent line, welded into the fuel filler tube, up high just after the filler tube enters the trunk. This line simply goes down through the trunk seal and ends inside the rear frame rail.
That would allow you to leave the vapor separator and lines alone, but yet go ahead and use the existing 1/4 line for return.
If you have a MIG or other source of CO2/ Nitrogen/ etc, you can drain the tank, and fill it with CO2 before you weld, or just yank out the filler tube and have at it.
However, before you do all this, you need to find out if your area has smog checks, you might need it.