Joel,
There are any number of ways to fabricate what you are attempting to add to the fuel system. The simplest way to do this is go to an aftermarket hat, I'll show you what that is in a moment. The hand fabriccated solutions all suffer from various maladies and failure points over time. They are time consuming and sometimes expensive (when you are all done) solutions to the problem.
There are a number of EFI suppliers today that provide all the functions and functionality you are looking for in a fuel hat that replaces (bolts in?!) where the OEM hat used to be.
The first thing I might do, if I were you, is determine the year and model vehicle your existing fuel tank came from. Then I would buy a hat for that tank if available. In the case of Ford tanks I would look at using a SN95 series tank like a 2000 through 2004 (possibly earlier and later also) Mustang used.
The fuel pump hat manufacturer I have used and currently use is Fore Innovations. Fore makes a family of fuel hats that will accept virtually all of the high and highest performance fuel pumps avilable from TI Automotive today. TI makes the oem pumps.
The hats allow the use of one to three pumps and bolt right on where the OEM fuel pump hat did. In your configuration a single 255lph pump will probably be more than adequate. The nice part is if you later hop up you powertrain you can just add more pumps. The hats also contain mounting provisions for the OEM fuel level sensor and the return line facility for return style fuel systems.
Here is a link to the 03/04 Mustang style tank, pump hat, click here=>
Fore Fuel Hat. Look at the blown up pics, roam around the site and check out the various supporting pieces he makes for EFI installations. The equipment is very high quality, all bolt together on OEM style tanks and a much easier, properly designed enhancement for your ride. BTW notice the fuel return in the top of the hat.
The base version of that particular hat is configured with two 255 lph GS342 Walbro pumps. Ford used two 190 lph (or so) pumps on the 390 HP 03/04 Terminators. Those fuel systems were essentially tapped out. Any additional power required bigger pumps or a Kenne Bell boost a pump. My guess is you are at the same or higher power level. Although a blown 390 HP will use more fuel than a n/a 390 HP, whatever you don't need can easily be returned to the tank. You will have a comfortable fuel reserve. Roam around the site. You will find a wealth of EFI equipment and some tools to make life easier — but most importantly the Fore stuff will get you away from those unreliable, nasty welded add ons you are currently saddled with.