If memory serves, the hard parts are nearly a bolt-over - provided you don't have C-clip axles! The c-clip axles ae retained internally, and don't have bolt flanged on the outside that will be used to retain the backing plates and the bracketry.
It's pretty esy to see which style D35 you've got - for starters, check arond the tube for four bolts to retain the backing plate for the brake assembly.
Failing that, next time you're changing the fluid, look at the side gears for a circular recess and a C-shaped clip around the axle shaft end (don't bother if you don't see the backing plate bolts. If the backing plate is welded on, you're likely to have a C-clip.)
Conversion from C-clip to retainer - the best way to do this is to change the axle housing entirely to a version with retainer plates - either D35 or D44. Failing that, you can remove the housing ends from the C-clip axle and weld on a set from a retainer plate axle, then bolt the retainer plates on from the donor axle.
Bear in mind that you will have to change the axle shafts when you change the retainers - since the outer bearings are pressed onto the shaft and are held in by the retainer plate rather than pressed into the housing. Also, the rollers for the C-clip axle ride directly upon the shaft (locally hardened,) while the retainer plate axles have bother inner and outer races upon which the bearing rollers ride.
I seem to recall a RW disc conversion using ZJ parts on XJ D44's, and there was a variation in the instructions for the retainer plate D35 to expand the application - seems to me like
www.madxj.com might have been the place to go for that - or just look about for 'XJ + "Brake Conversion"'
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