Hi Enigma
LX 470 is the best SUV no doubt, but it comes only in 4.7L V8 gasoline engine. Lexus represents an elegant and luxurious class with comfort, pick and quiet operation. With a diesel engine these are difficult to achieve (especially noise and vibration is problem) Moreover those who can afford Lx 470 are not bothered about cost of fuel.
Land Cruiser Cygnus is identical to LX 470 but bears monogram of Toyota as it is meant for domestic market of japan.
Thirdly, it is not at all advisable to put a diesel engine in lexus body, it will never give the feeling of a Genuine lexus,...... or changing lights of land cruiser and fixing a lexus monogram can never convert LC into a lexus.
Akbar Khan