Okay, the Poly kit and the Currie kit are exactly the same on the driver side (diff housing jj joint just presses in) but they do vary on the pass side. Currie, as was pointed out above, has you cut the existing mount down slightly at an angle then slide the new tower assembly inside the existing mount and weld it up (you also drill out a couple holes for some plug welds too).
Where these two really differ depends on how your gonna run your front axle. If you are gonna truss it with say an Artec truss kit, I highly recommend the Currie kit as it has less of a gap around the tower if you install it per the instructions, however, you can always cut the existing tower a little higher so that the truss wraps it tightly.
The Poly kit has a much narrower tower and the gussets provide the lateral support. In a situation where you use an Artec truss it leaves a huge gap to fill, plus you are spending a little more money for some gussets that you wouldn't need if you use a truss.
I refer to the Artec truss only cause I think it's really the best setup for our axles and the most complete kit I have used so far.
And further, yes...the jj's really allow a shit ton of flex. I get no bind whatsoever with them and I always recommend that the front housing kit be done when adding a truss or even just doing a simple gusset addition. It free's up the front end so much and things feel very smooth.
If someone were to order a Clayton lift I would only get it with jj's. Clayton and RK both have good flex joints, I'm just partial to Currie jj's myself is all. I have had no issues with the older style RK flex joints and haven't had enough of the newer joints out there to judge them yet. I'm sure they will be fine though based on my experiences with RK.
Also on a side note, I suggest you disassemble the jj and weld it up without the guts so you don't melt your bushings. They are very susceptible to melting even with just a little heat. You will be adding a few tacks to the backside of the driver side joint and of course your putting a lot of heat on the tower to get it all set up properly. Not only that but then you can see for yourself how easy it is to rebuild the joint when and if that time comes for you........
Originally Posted by van7559
I can bury my pinky in the rear, and just barley feel it, the front is a little easier, but still seems low to me!
I fist fuck life with a nuclear powered pneumatic fuck hammer for 60, 70 hrs a week...