NAS Defenders were all sold as v8 petrol only. Some of the older ones (usually series, like >25yo to stay legal) have been imported with the stock 2.5 NA diesel. Some people have done diesel conversions on their defenders. Just for reference, I got a quote a few years ago to do a turnkey diesel tdi swap into a D90 - $20k give or take. Thats about the same price as a truck costs to start with. Yes, this was a high bid (some of you may even be able to guess from where
) and no I've still got the stock v8 petrol motor in my truck.
As for swapping out the stock nuts and bolts - that along with just about everything else that would not fall under 'standard maintenance' (and I include the oil cooler etc lines in that
) are pretty much optional. Assuming the items in question are in good shape and not worn out, your truck will run just fine as is.