The newest Mercedes common rail diesel has an alloy block, but was made a V6 instead of an inline, maybe because the bore spacing was made thicker than the iron blocks, I don't yet know specifics, it is likely overengineered, it is too expensive. I have heard that the alloy 3.2 CDI V6 makes 376 ft. pound torque from 1,600 to 2,800 RPM which is excellent for that displacement.

I think the 5.9 Cummins might weigh closer to 1,100 pounds fully dressed, although it is a heavy duty truck block adapted for light trucks, it's too long for most passenger cars. The Cummins 4BT is a four cylinder version. Mercedes CDI technology will likely appear in Chryslers, although a motor designed for a $50,000+ car might be kind of expensive. The 2.7 inline five is iron and pretty heavy, but also has decent torque numbers. I think the alloy 3.2 V6 has about 220 hp and is designed for a 3,800 pound E320, could be a good Valiant swap in future years with $5 gasoline. Mercedes diesels outlive the cars. The official E320 EPA sticker says high 30s MPG, but some report up to 50 MPG highway with these.

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That depends. With the later versions, the spot that usually needed the most attention was actually the injection pump and NOT the basic engine itself, as was the case with the early ones. Hardly worth the effort to keep one running, but definitely possible.

For that matter, I never see any of the later (and better) normally aspirated GM 6.2L diesels either. Normally aspirated diesels really aren't worth the headache, except in applications like a tractor or stationary generator.

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