From Land Rover International Magazine (which has been
running articles on LPG conversion since LPG is 1/2 price of
petrol in UK and many LRs have 3.5l V8s) ...

It is possible to convert diesel engines to LPG, but very
expensive, as the compression ratio has to be lowered and a
spark ignition system added.  It would be cheaper to buy a
petrol engine and convert that.