Mustang tanks can be purchased new set up for fuel injection ,an external pump is easier to hook up ,especially if you ever have to work on it . I did a 78 ford F100 in 1987
using the 5.0 from a thunder bird .Back then i used the external pump from a 87 f150 that mounted on the frame rail ,now you can get pumps from Holley ,and other makers so it is simple now .
The 60s ford f 100 have an in cab tank behind the seat ,i would change that to a frame mount tank ,dont like the idea of getting a Gas bath and set on fire .
Running fuel lines is not a problem ,i ran another line side by side with the fuel line for the return line that dumped into the fill neck but extended a few inches below that