Considering the global nature of manufacture, I don't think that you could really call any of these truly American/Japanese/German/British ect... I'd personnaly rather see the truck going up and down the road being useful than rotting in a field or getting smelted down.
The Isuzu engine in the transplant that DieselM37 has may have been a much better deal (price, availability, parts supply, etc.) than any other diesel that most of us think about using in a repower and since he is in Canada, his issues are a little different than those in my area.
Even purchasing a US name engine built in the USA gives one something that isn't what it appears to be:
The engine in my M37 was built in North Carolina, but the block was cast in Japan (Komatsu joint venture with Cummins...), the turbo was built in Britain (Holset, aka Cummins Turbo Technologies), fuel injector pump is German (Bosch). I haven't tried to track the sources of the rest of the parts...