The Ford 2.2L diesels were kinda weak or had a bad rep, but the 2.3L turbodiesels weren't too bad, if I remember right. The old Nissan diesels are good, as well as Isuzu, Volkswagen and Toyota. You could get really oddball and find a Kubota, John Deere, or Caterpillar 4-cylinder diesel and swap it in. I think for power and economy, though, one of the best I have seen lately would be the Volkswagens (1.8/2.0 TDI Jettas) as far as smaller engines. Just remember, though, diesel engines are usually heavier, so you may have to level out your front end and whatnot. Wouldn't surprise me if you could "tune" an 'original' 2.3L Ford turbodiesel engine.... and your best bet on finding one would probably be in Canada.... good luck importing that!