Am I the only one here that doesn't care about hacking the floor? As for the gas tank, why not just replace the main tank with a sub tank? It will help distribute the weight better and give you room to make the upper rear links the same length as the lower rear links. Correct me if I'm wrong, but that would help with articulation?
that is the answer but...
all you need is a tank made to take the factory fuel pump-unbolt it from the oe tank and put it in the rear tank. also a harness extension for the fuel pump. new lines for the tank. a new filler neck and hoses. brackets., etc..... it may be easier to put a narrower tacoma tank or other cheap tank in the oe location. but the issue with hacking up the underside of the cab is still going to be a sticking point for most. a planitary box, and especially one that was clockable, would fix that problem. a 3.8:1 atlas would be nice also.