I'm still not clear on what kind of a look you hope to achieve. Are you clear on what a unibody is? Except for the doors and front fenders (which are bolt-ons), most of the body panels, including the roof, are stressed skin members that are part of the structure of the XJ. It's not like a Blazer or a Broco or an Explorer that has a body bolted to a separate frame. Therefore, there are no kits, because there's really nothing to mount a body kit to.
Sean (OneTonXJ) has chopped his XJ down to little more than a rolling floor pan -- but he restored (actually increased) the structural strength with a multi-point roll cage. Beezil's customized XJ also has a cage tied into the chassis for stiffness. I don't remember if Borton's uses a cage or not, but I'd guess it probably does.
All those guys wanted a cage for stiffness and for roll-over protection. If you're after a street look, you may not be as concerned with the protection a cage provides. It certainly interferes with interior access. I just don't see any easy way to take panels from some other vehicle and attach them to an XJ unibody, but as I said I really don't have a sense of what you want to create. To be honest, it sounds to me like an XJ (or any unibody vehicle) is not what you should be starting with. You should probably be starting with a vehicle that has a real frame, and then you can bolt on any body kit you want. A Jeep CJ or Wrangler has a separate frame, so you could take one of those to get a 4WD platform, and replace or customize the body to your heart's content.