Lift up the rear of your XJ. Allow the rear axe to droop down (with tires off and front wheels blocked off). Loosen teh Ubolts on eth leaf springs/axle tube on both sides to allow for a small amount of space between the perch and the leaf packs. Then place the juack under each side of the axle tube by the shock mounts and remove the Ubolts from that side of the axle. Slowly lower the rear axle to the ground. Then do the same to the other side.
Remove the factor leaf pack clamps from the leaf springs. Place a large C-clamp near the center pin (I say pin, but it's a bolt with a smooth allen head) that holds the leaf pack together. Unbolt or hack saw off the nut of the pin head and remove the pin, then SLOWLY open the C-clamp. Remove all the leafs under the main leaf.
Take the S10 or Dak pack and put the C-clamp near the center pin. Remove the C clamps from the leaf packs. Remove the center pin and SLOWLY open the C-clamp. Now, take the leafs that are under the MAIN leaf of the S10/Dak packs and add them to the main of the XJ that is now hanging on the XJ. You will need a LONG center pin. Rusty's offroad sells a pack for $5, but check around local for parts stores or even the dealer for replacement pins.
Thread the pin from the bottom leaf up through to the main leaf of the XJ. Put the nut on pin so that the nut will rest on the main of the XJ. Use the C-clamp to slowly tighten the leafs together as you tighten the nut up top. Do the same on the other side.
One at a time, bring the axle tubes up and attach the Ubolts to allwo the axle to hang on the new packs. Then slowly tighten up each side and make sure the head of the center pin goes in and seats on the leaf perches on the axle tubes.
DO NOT TRIM THE PIN yet. Allow the the vehicle to settle and take a measurement. From the middle lower section of the flare to the center of the wheel it should be 17" stock. You will want about 20.5-21" go get about 3" once it settles. If it doesn't net that much lift, you can take the pack apart again and add one of the XJ leafs pack to the pack.
For the front, you can use V8 ZJ springs or F150 V8 springs to net about (roughly) 2" of lift. Run one 1 3/4" coil spacer. Go to a junk yard and pick up a set of stock spring isolaters. They are 5/8", so a little over 1/2". Personally if I was you and you plan on a winch, I would SERIOUSLY consider buying some Heavier spring rate 3" coils from Rusty's offroad. They are about the cheapest around at about $125 a set (double check that price, it's been awhile).