Don't you think most of that would not be true if the diesel engine had a cast iron cylinder head? It's likely that overheating the diesel engine would not be too much of an issue given it does have a cast iron block and head. The most damage you could really do to a diesel engine if you overheat it is blow the head gasket. But since the 4D56 and 4D55 are cast aluminum head diesels this is not really true of them being under that category. I'd still think that doing a 4D55 diesel swap would cost you less than doing a whole rebuild of the 2.6 gas engine. If you don't have your mind set on getting a 4D56 to power your vehicle you should go with the 4D55. Seeing as the 4D56 is going to have to be bought from a foreign country, that is why the cost will be so much. You'll be spending a lot of money right up front before you even start the conversion. Since the 4D55 was available in the U.S. from 83-87 it will be easier to do a project with one of them as a powerplant. Basically, all you have to do is buy the diesel engine. If the accessories (transmission, radiator, etc.) between it and the 2.6 gas are the same then you already have most of the parts to accomodate the diesel. I'd stick with a diesel project that's for sure.