lowbox is right, keep the lift to a minimum, much more stable.
defenders have heeps more room for uptravel than their rangerover cousins. some guys run 34" jt2's on stock suspension in defenders and they only just rub. (with the right offset rims- disco wheels offset 25mm. more than stock.)
the front toy conversion works a treat on defenders(1" spacer)
rear gq needs a pin to eye convertor at the bottom(very easy to make)
you will probably need to lift the rear top mount. i have seen a 10mm steel plate used here.
rovers are cursed with shocking rear bush angles for greater than stock articulation. i was told lra (rangie spares) make and sell a nice rear shock mount kicker thats excellent for restoring bush geometry.
4"lift is very high. unless you widened?? the track by double that(8") a stock height defender with the same size tyres would outdrive you every time off-camber and sideslopes.
(easy to find at the mall though

)