I've done 3 diesel transplants in my various rangies over the years.
1st: 85 RR fitted Mirtsubishi 3.3 Turbo and R380 box- quite a lot of torque and seemed ok for towing ONCE you rode the clutch to get moving! Heavy at front end ( weight of 2 V8's there), spoilt handling. No rev range.
2nd: 93 RR- fitted a 300TDI and retained the ZF auto; similar weight to V8 so no air suspension problems; tweaked it with bigger intercooler, more fuel, slightly more boost. It went well- same as 3.9 V8, but blew lots black smoke when full power! Easy transplant as no electronics to worry about, really all the change to electrics was a power-off solenoid!
3rd and still current: 94 RR soft dash LSE- fitted a TD5 and electronic auto, went the hard way ( not all Disco wiring loom) as I retained EAS and true Wabco brakes/ETC.
Power upgrade, better exhaust and this one like a 4.6 V8! NO smoke! As I've used this car for heavy towing these last 5 years, have destroyed the ZF 4HP22, so now upgraded to 4HP24 and bigger torque converter. Lower stall/not sounding so busy now, it feels a lot stronger, quicker acceleration.
Because of the rear legroom of this car, I doubt I'll ever get rid of it. Still no RR has same amount of interior space. ( Unless I can find another soft dash LSE AND a TDV6! Interesting thought?)