As someone else already said earlier, you can pick up genright tanks used for a lot less than buying one new. I scored mine, which came with the sender/pump unit and the sender ring tool, from a guy in NC for like $500. Granted finding a used genright comp tank would be ideal, but there appears to be more used ext tanks out there for some reason or another. Another option for mounting a fuel cell would be to sink it into the rear floor of the tub. A few guys I used to wheel with in Colorado went this route, but also tabbed a skid for the bottom of the cell even though it didn't hang lower than the rear of the frame if I remember correctly.
As for the link situation, do the triangulated four link and be down with it. I couldn't even imagine wasting time trying to relocate the rear trac bar, especially with as many flavors of bracketry there are out there that you can use. Just remember that if you're going to keep coils in the back you will need to move the buckets back on the frame and will more than likely need shorter rear coils depending on how far back you go. Also go ahead and outboard your shock mounts using the weld on rear mounts that you notch out the frame and then french the new mount into the frame. This way it will be easier to upgrade to coilovers, air shocks, or ORIs in the future.
As for the front stretch, as Brooks and a few others said, its kind of a pain unless you're going to full hydro. If you want to squeeze 2-2.5 (3 tops) inches in the front you can move your buckets and shock mounts back on the axle, cut off the stock trace bar frame side mount and replace it with a new shorter weld on style (I used TNTs), and run a flat or twisted pitman arm (I used the genright set up). You will need to run a 1 inch body lift for the pitman arm to clear the bottom or the radiator, or you could always see if you could move the mounting holes up to create enough room. I've also seen guys extend the front part of the frame an inch or two in order to move the steering box further forward and also rotated flat to achieve more front stretch.
Anyway, my 2 cents on the subject.