You should be able to find a late model 3.2L or maybe a 3.5L on your side of the pond, from another Isuzu model. The Trooper, Rodeo and Amigo all had the 3.2 at some point in the US (I don't remember the UK names - Bighorn for the Trooper - not sure about the other models - Vauxhall?).

I believe the same motor was used in some other non-Isuzu models as well - have you had any luck in the scrap yards?

-- Best, John