The SHO V8 is a duratec block with two cylinders grafted on during the casting process. The heads are Yamaha, and probably the intake as well, although I do not recall.
The SHO V6 is entirely Yamaha, and the block was based on either the Vulcan or Essex, which ever one was NOT the basis for the Duratec (Sorry, I can never remember which is which).
As part of Ford's agreement with Yamaha, they apparently reserved the right to learn from and possibly emulate Yamaha's technology.
The duratec was designed in Dearborn, the electrical, induction and exhaust in England, and packaging in Germany. I think the packaging development (and the fact that there were Duratec motors in Germany) led to the popular belief that a German company aided Ford in the development of the duratec, but I've never found any indicators that Porsche was busy in Dearborn with Ford during the design phase of the motor, or that they assisted Ford operations in Germany. At the same time, Porsche, and many other automotive mfg's do offer consulting services, and are often willing to work with most any company as long as the price is right.
No matter how it all fits together, the Duratec has turned out to be a world-class performer like the Yamaha motors (the swedged V8 cams being the only exception) in both durability, power and mileage. The duratec is the best mass-produced low-cost V6 on the market. And looks to continue holding that title for some time with Ford's next iterations, the duratec 30 and 35. It also holds the title of smallest and lightest V6's.