The FA600 drop arm certainly is an easy solution, Since you say you're not using it that hard offroad, it'll probably work fine for you, but certainly there are some other options (if you're at 6" of lift, the FA600 would still leave you with a 2" disparity anyway).
Ranger TREs have a M22-1.5-R thread (passengerside), and a M20-1.5-L (driver side). I have yet to see anyone offer threaded bungs that accept those threads, everything seems to be 7/8"-18 or 1"-18 (betting metric thread taps in those sizes are not easy to come by either).
I continue to hear complaints about continued bumpsteer with the Stonecrusher style setups. Though I have not run the setup personally, my gathering is about all it does is eliminate the extreme tire wear (toe-in/out variations) you'd otherwise have with the stock linkage & too-short pitman arm, but little else.
My suggestion is to just get the Superlift Superrunner steering kit (K-link style) and then modify it by dropping it's centerlink down to where it belongs (same plane as your axle pivots).
It is a shame you have to buy something brand new and then hack it up, but even in spite of that it still seems like the easiest option that actually works well.
Alternatively you could build something from scratch basically copying Superlift's design, and maybe improve on it in the process (such as lengthen the upper tube of the idler arm so it won't deflect on it's bushings as much).
I've also seen a couple guys build setups that are like a hybrid of the K-link and a crossover type setup (similar to a swingset style setup, but with a centerlink & idler arm instead of swingers).
Two examples here:
http://www.therangerstation.com/forums/showthread.php?t=119782
http://www.explorerforum.com/forums/showthread.php?t=337182
IMO, I'd just keep it simple and center-mount the tierods. That's how mine is and I've had no complaints with it.
You need the FA600 Drop pitman arm , I would Suggest Getting the Supper Runner Steering Kit as well .
Cannot use both the FA600 drop arm and the Superrunner kit... One or the other.