How It's Made: Cummins 6. 7L Engine
How It's Made: Cummins 6. 7L Engine - Diesel Power Magazine
Craig
Nice article on the assmembly of the engine, but it doesn't really answer the OP's original question on block origin of manufacture. In fact, the article states that the blocks are cast "off site", but no mention of where said site is. There is another recent thread on TDR indicating the blocks are cast in China, can't speak to the truthfullness of such, however. The fact that the article (and/or cummins) avoids mentioning it, probably lends credibility to the China thread.
In regards to your question, when I was on the tour at the Columbus mid range engine plant our guide told me the blocks were made in China. He was a knowledgable fellow and had been with Cummins for some time. I have every reason to believe he was telling me the truth.
I would love to find proof that contradicts what he told me but yet I have not found any.