Having a pile of used leaf springs is an advantage when building your own packs. I pick up leafs whenever I can, especially if they are free.
You need to find a few springs that are pre-drilled for clamps.
You can drill and countersink them yourself but good luck with the hard spring steel. Pre-drilled is a lot easier.
If the leaves are too long, you can diamond cut them with a grinder or a cutoff saw. Cutting the springs allows you to space the spring length exactly the way you want.
My packs have 6-leaves, all 1/4' thick, each with to two rivet-on U-clamps clamps and one OE-style rubber-wrapped clamp at the rear.
I added the rear clamp to help tame the wheel hop and it works fine without limiting articulation. The clamp is just snug enough to keep the leaves from separating. The rubber wrap stops the rattling.
Inter-leaf friction is controlled by full-length 2-1/2" wide plastic liner (H-shape) from Eaton Spring.
http://www.eatonsprings.com/ Call to buy.
This stuff is great. It produces a smooth ride that does not degrade over time the way spray moly and other dry lubricants do.
Building your own springs is hard, dirty work that allows you to inexpensively address your XJ rear suspension needs better than most off-the-shelf aftermarket springs.
If you are picky about getting the right spring combination, be prepared to spend a bit of time to get it dialed in.
Buy extra center pins and a set or two of U-bolts.
I started building my own several years ago after reading Goatman's past postings on DIY leaf springs. It's worth searching for.