rear shocks on the xj, start spraying the bar pin bolts with plus gas or a proper penetrating oil NOW not WD40. these four top bolts will shear. then either punch the captive nut out and use a nut and bolt with stud lock or drill out the bolt and retap to a metric thread 6mm or 8mm, cant remember the size. the ones on mine are nut and bolt affair.
as for shocks it depends on how big your pockets are if sourcing from the uk. for the price of two shocks you can get a set of four delivered from the states.
i have a set of sky jackers but they creak and squeak so thet will be replaced at some point for a set of Ruby express twin walls