I must admit I am more than a little amused at what you plan to do in the short term with it, let me explain. XJ with stock drivetrain (regearing only) + 35's/37's = poor choice. First the XJ with its wonderful 4.0L engine is good at many things but sand/mud is not one of them. Sand and mud are similiar in that power to the ground means the difference between moving forward and sitting still. Even with better gearing the 4.0L simply isn't adequate for serious mud/sand when you add in unsprung weight to compound the problem.
All "kits" have good and bad. You'll have to decide which is best for you. Looking at the options based on what I know I would consider either the RE kit or the TNT. I think the radius arm setups have been around long enough to prove their worth. TNT's setup is nice for the clearance but I can't really say much else about it. RE has always had really good quality products.
A few things worth note are what type of joints are used. Generally speaking a joint that articulates should be better but each one has positive/negatives.
There are a few types of bushings used. Rubber or poly mostly. Rubber is better flexing and for less noise but can tear if pushed too far. Poly is firmer but can be noiser and can also tear if pushed too far. If I had to choose I think rubber is better. In the case of one of the listed kits (Full Traction) I must say based on a friends vehicle I am very disappointed in the bushings used by them. They seem to quickly almost shrink or wear allowing the sleeve (through which the bolt goes) to move. This causes a noticeable thud when accelerating or stopping. Simply using a better flex joint (listed below) would be preferable. RE in some applications use stock like bushings (or used to) which if used within a certain amount of travel work well but if you add in longer shocks or drive them too far they will tear/wear out fast. This happened to me with short arms a 30" extended length shocks. I fixed the problem by using arms with flexable joints at both ends like listed below.
Heim joints are non-rebuildable/replaceable (have very little to no give) but more exposed to dirt/dust damage, RE's Superflex joints (they use a hard bushing material that has more give than a heim joint but less than a Johnny Joint) are rebuildable/greaseable and should be a little better, and finally Currie's Johnny Joint is a rebuildable/greaseable (uses a bushing with more give or noise isolation. Personally I consider the RE or Johnny joint to be the best to use. Depending on whether or not noise isolation/give is important for your use would be which I'd recommend.
Another thought is while softer springs are better for the rocks/flex/ride it occurs to me that stiffer springs might be better is the mud/sand.
An 1" or so clearance shouldn't make a real difference since the stock crossmember I would think is as low or close to any arm setup you use.
Just a few thoughts to ponder. I might add more later as time permits.
Mike R