I run the FITECH on my small block. Same concept, very happy with the drivability and performance, easy to hide.
I went for the return line to the tank, so the fuel pump stays constant. Yes, an extra line, but after trying both thier surge tank set-up, and a single line, I found the system worked best with the return line. Use the 255 lph pump.
Many companies make gas tank adapters with pumps for the Mustangs.
Also remember under the hood you'll have alot of extra wires, so route carefully, add extra GOOD grounds.