Actually, that looks rather decent (see my atrocity below). There isn't much else under the car that is lower (though the picture makes it appear lower than it is) other than the rear floor well. After all how many are going to look under the car anyway??? I used the Ford F-150 external pump and the filter from my Turbo Coupe. That pump has a sheet metal housing with cushioning and is a lot larger.  I'd think that to got the tank to seal you would have to weld  a portion of another "in tank" arrangement to the Pinto tank. That in itself is a danger plus the re-enforcement ridges would probably be a nightmare.

 If you are concern about the return line, some have tapped into the filler neck.. I soldered an additional tubing into the fuel sender. It melted the nylon seal but 7 years later it is a testament to how well JB Weld holds up immersed in gasoline.  Whatever you do, be careful and remember you do at your and others own risk. BTW, I'd also recommend a fuel shut-off switch. The impact activated type can be found on just about any Ford.

Is it possible to put a fuel pump in the tank for my EFI swap on my 74 Wagon?

Conceptually yes, but you will run into the same problem that most classic cars have; the lack of a sump in the tank will cause pump starvation when the fuel level gets lower*. If it doesn't cause noticable running problems, then it incrementally shortens the pump's life. Holley has a new fuel pickup sock that is supposed to cure that, but it's big money.

*This happens with external pumps as well for the same reason. The de facto solution is to run a low-pressure lift pump that can tolerate short periods of dry running and use it to fill a "surge tank." The surge tank then functions as a fuel accumulator and air separator that supplies the high-pressure pump. I plan to do this eventually, but for now I just keep the tank full above roughly 1/3.

Other options are to use a sumped pickup assembly like the Yogi's one linked by Hairball or a weld-on sump available from most speed shops. Unfortunately both require modifying the tank. Pinto wagon tanks are not available new anymore if the modification goes wrong. They are also galvanized which adds another layer of consideration to welding on one.

I don't know about wagons, but a hatchback's tank top fits right against the trunk floor so a pickup lid and fittings simply won't fit there. EDIT: I looked at some old photos of my tank and there's a recess that might have enough room.

   I cut around the pump mount area of a late 80's fuel tank,cut a hole in the top of my 77 hb and welded it in place. this allows you to use a in tank pump. I had to shorten the filler pipe to clear.I plugged the fuel linesl  outlets I also baffled the tank