if you feel like wheeling your pajero then go with the locked Paj...they are pretty rare in a diesel!! If you don't plan on wheeling it religously and don't want to ever change a timing belt...the 2.8 is the better choice. as with any decision there are pro's and con's....You just have to decide what you want to do with it and what suits you best.

Parts availabilty on the 2.8 is a bit harder too I think, I know the 4m40 came in some CATERPILLAR miniature excavators but industrial and automotive engines are usually different in quite a few ways, even though they are the same engine.

personally I would stick with the 2.5 Diesel as that engine has been around for 20(ish) years and has proven its longevity to many people. I read a guy in australia has over 1,000,000KM on his 4D56 and only done routine maintenance on it.