I didn’t imply that it could not be done. Correctly done with out fabrication. I consider the genright tank a fuel cell.I believe he was referring to an LJ, though even in a TJ you can certainly stretch 5" without a back-half kit. There are also a handful of gas tank options that don't require going to a fuel cell (not saying any of this is smart or bolt-on, just that there are other ways to skin a cat).
If you squeeze out a couple inches up front and the rest in the back it could be done.