If you look at the stock XJ front axle you will notice the axle center is 2.5" or may be 3" rearward of the spring pad and that the lower control arm pivots are well below axle center. I moved the axle forward, directly under the spring pad (also adding lift), rotated the control arm brackets on the axle up level with the axle height first (helping with arm angle and ground clearance).
Next step was to put the big tires on and extend the bump stops till the tires didn't rub (just take fenders off, tune later). With the axle against the bump stops (bottomed out) and all your brackets tacked on, you measure hole to hole for your link length.
The reason I picked that 2.5" of forward axle movement is that the steering (pitman) arm still clears the Panhard mess with the stock axle, arm length and box location. There are other methods, this was mine.