The 2.8L Isuzu diesels are good engines and viable options for a LR. My preference would be for the turbo version.
4JB1: 127 ft/lbs, 76HP
4Jb1-t: 149 ft/lbs, 91HP
2.25 Series petrol: 120 ft/lbs, 70HP
The 4JB1 NA is similar in peak power and HP to the series petrol engine, however, the economy and the delivery of the power would be better. Not worth it IMO for the NA engine, unless your current engine is dead.
For a series truck, it would be ok, but not revolutionary. For the NA, the peak torque and max fuel efficiency are both pretty close at ~2200 and ~2050rpm respectively. An LT77 in good nick would be good for the power, but you would need to run the numbers for gear ratios etc. to make sure that you will be running at the proper section of the power band. I would strongly consider going with the T.