My vote goes to the Isuzu, it'sa basic direct injection, and gives good
response. I would advise you not to get the Isuzu 3.1TD, while it is a good
motor that will also last, my persoal preferance is the more responsive
direct injection to the more laggardly but more powerful indirect injection
3.1 unit.
If you can find a 3.0TD 4jx1 cheap snap it up but first ensure all the
warranty recall bits have been done, namely the injector sleeves have been
replaced (fixed on '02 onwards engines) and the oil pickup in the sump has
been rerouted and the turbo has been done.

I am not sure where you are located but I assume based on the URL that it is
in England. That being the case I would suggest that you try
alt.fan.landrover if it is available on your news server. The regulars on
this group, most of which are UK based will be able to give you a lot of
more localized advice. Personally I would have a very good look at a 300Tdi
motor as this might bolt straight up with no cutting, welding etc (not an
expert opinion).  If that is the case then you would probably be better off
paying a little more for the engine and saving a bunch of time and effort on
all the usual conversion paraphanila (adaptor plates, clutches, flywheels,
engine mounts, broken knuckels etc, etc. etc.)

I did a Nissan LD 28 conversion on my serIII and I am finally quite happy
with it, but it was a lot of effort, a lot of money and a lot of fiddeling
to get the cooling right. It is amazing how removing the Warn 8274
revolutionized the cooling. I will never again put anything in front of the
rad on any vehicle I own.

If you are UK based what about an LPG conversion? I have no experience of
this but I gather the running costs are similar to diesel but the conversion
costs may be substantially less.

Regards
Stephen

Better sell your car and buy one diesel, but be cautious with the VM engine,
they aren't reliables.

If you persist, perhaps a 2.5TDI VW engine is a better solution, they are
very common in Europe. Even a 1.9TDI is a good choice, there is a version
with 150HP.

Regards.