The MERCEDES 5 cylinder OM617 is a tried and proven diesel swap into MANY different platforms. You can probably buy all the adapters and such needed to drop it in, it is such a common and popular swap engine. The newer MERCEDES diesels are also good canidates as well. The newer 4&5 cylinders are smaller, lighter, and far more powerful. The newer OM603 is supposed to be close to the same length as the OM617 5 cylinder, almost twice the power, and about 1/3rd the weight. Only downside is they had ALOT of problems with them over the years(early 86-87 engines were good, but heads commonly cracked on them. Then the later models from 89 on were a larger displacement, and had problems with rods that would lead to engine failure). The OM602(newer style 5 cylinder IDI) is supposed to be a good engine, and was used I believe from 86 to sometime in the mid 90's in the states. Another thing is they are not that popular in the MERCS, so they tend to be cheap. Theres LOTS of swap options out there, the question is, is your rig worth doing it to? If it is I would definately look into the MERCEDES engine for a vehicle the size of the ranger. The 4BT is more suited a full sized truck than a RANGER as it weighs close to 1000 pounds IIRC.