I have a dual set up ihn my 71. For you, install a saddle tank from a 55-71 CJ. Run both fuel and return lines to a petcock between the seats. You can use either a manual one from a late 70's Ford or an electrical one from a late 80 truck (both will have a fuel and return line, although the manual one's are rare and hard to find). I believe that a switch from a 87-97 Ford diesel will also work. As for your fuel gauge, if the switch won't flip it in tandem with the tank your using, simply mount a three pole switch next to the speedo head and lable it main and aux. Run the power wire to middle stud, the rear tank to one and the aux to the other(be sure to ground the aux tank sending unit). You will need to remember to switch the tanks both manually or the fuel gauge will not be reading the thank your running.