Grand Wagoneer front leafs have lots of arch and are still flexy, add a thick bottom overload leaf from a truck leaf spring pack and you'll havet he best of both worlds. Stack these on your stock XJ main spring.
My old XJ had 8" of lift and used a stock standens pack with the military wrap, a 3" AAL, some Grand Cherokee front leafs(2) and a thick bottom leaf from a Dodge truck. Flexed like crazy but still could carry 2 kids, 2 dogs, and problably 150# of gear in the back and a 33" spare on the roof.
Grand Wagoneer leafs are getting hard to find. Try taking the 2nd leaf out of a 1/2ton truck and sticking it in you leaf pack under the main leaf. If it has the thick, straight short leaf on the bottom then add this to the bottom of your leaf pack as well. Those 2 springs will add 1" of lift just from the thickness of them. The short leaf will only let the pack straighten out at most, won't allow a negative arch when loaded heavy.