The 3.0 Duratec engine is a Ford design, with some ideas from the smaller 2.3, but it is a complete Ford design. The 3.0 Duratec was assembled at the Cleveland Engine Plant (I think plant 1 actually) in Brookpark Ohio. This is now the new home of the 2010 + Taurus engines as well.
the SHO 3.0 and 3.2 engines were designed and built by Yamaha and ford put them in the Taurus. the V8 SHO engine was a joint effort between ford and Yamaha, the block was built by ford using a cosworth casting process and then shipped to japan for final assembly by Yamaha then shipped back to the states to be installed. the Duratec 3.0 is all ford design again using the cosworth casting process for the block. and of course the Duratec 3.5 and 3.5 turbo are all ford design. the Taurus has never had any Mazda derived engines in them though Mazda has used some of ford Duratec line of engines in their vehicles.