Bill,
I don't know which brand EFI system you are looking into or which basic fueling model return style or returnless you are considering, so the following comments may cover some obvious ground.
The various in-tank fuel pump models available to you break down into two different families;
- The first is the return style employing a separate return line entering the tank at some convenient location on the exterior. Because you do not have an EFI tank, you will need to fabricate this entry.
- The second is the returnless style, where the pumps are installed in a vertical basket that enters the tank through its top surface and is sealed with an o-ring or other gasket and uses no returl line whatsoever.
There is any number of EFI providers that supply this type of pump 'basket' today. Many EFI system providers have incorporated design idiosyncrasies either intentionally or for lack of product design forethought that makes their fuel pump baskets favor their particular EFI product families.
I have a favorite provider for these types of components, that is EFI system and manufacturer agnostic. The provider is Fore Innovations. While they provide pump baskets that are bolt-in specific to the user's existing OEM fuel tank, it is also possible to use them with a weld-on flange for aftermarket fabricated fuel tanks. This is a link to their website and one of their Ford fuel tank multi-pump style hats.
Click here => Fore Innovations
That particular pump basket is for a returnless style fuel system. Today that I am aware of the operating logic for that type of system is only available in OEM ECU's and MS3Pro ECU's from DIYAutoTune. All other ECU manufacturers will only provide systems with return-style fuel system logic.
If the election is to use a return style system, then the plug in the return line hole in the pump basket is removed and an AN fitting installed for your return line.
The Fore baskets will support any in-tank pump commercially available today. When you explore the pump options on his site, you will see the range of pumps available to you as the fuel system designer.
If you have a space consideration where the tank is too close to the trunk floor, you can build a mounting flange, with a recess allowing the basket to clear the flooring, that can be welded to the tank and use an angled fitting to attach the fuel line.
As I have mentioned in other postings, the MS3Pro EFI system can be purchased to work with an OEM Ford engine and under-dash wiring harness making the installation both more straightforward and less expensive while using a 100,000 mile OEM harness that will outlast yours and several subsequent owners, ownership of the vehicle.
BTW in the FWIW bucket, the MS3Pro plug-and-play systems come with an excellent base tune using the OEM Ford returnless fueling model. This is the MS3Pro system that both supports the returnless fueling model and also comes with the base tune as a stepping-off point.
Click here => MS3Pro for Mustang GT
Here is a video of the install in a OEM vehicle that is litterally plug and play,
click here => Mustang 1999-2004 MS3Pro Install
The video is 7:45 mins long.
This next video is the follow-on first start video after installing the EFI system in video #1. This video is 10:51 mins long.
Here is the video of the first start experience right after the install,
click here => First Start Experience
You'll need the pump basket from Fore, the OEM wiring harness out of a 99-2004 Mustang GT, an FPDM (fuel pump driver module) and the FRPS (fuel rail pressure sensor) out of the same Mustang GT you got the wiring harness from, a set of aftermarket fuel rails and an MS3Pro PnP ECU from DIYAutoTune.
There are stunningly good 10 to 15-minute Youtube videos that do an excellent job of showing how the system is tuned. Of course, it comes with both tuning and data logging software so you can test, modify and check the results of your tuning efforts.
I hope this helps in your search.