I have a 2.5 NA diesel in my truck. As Roamingman says, as long as you don't plan on zooming down motorways at 70+ mph, then you will be fine (and to be honest, given the handling characteristics of the defender, I think going over 60 mph is a bit foolish...not what it was designed for). I have had 3.5 V8 defenders, a 2.5 petrol Santana, a couple of 2.25 Series IIIs, a couple 300/200 tdi's and to be honest, the 2.5 NA diesel is my favorite so far. It is simple, rugged, has lots of guts at the low end and will cruise comfortably at 60 mph...unless there is a long hill. When I bought this truck I thought I would upgrade to a 200 tdi but having driven it for 2 years now I am happy to stay with the 2.5 NA. It took us through France and Spain last year, will do Morocco this year...and eventually will take us across Asia to Malaysia and on to Australia.
"We've got a date with Destiny...and she's ordered the lobster!"