I have read the brochures and found that the TC 2.0 gas engine can be ordered with a hardened intake and exhaust valves for possiible LP or CNG use later on. But after talking with 3 different dealers, I've been told that they cannot find any TC's with that option.
It seems that the brochures are a bit optimistic on some options. It has been my experience that they show some as being available, until such time as you actually want the real option and not a picture!
Hopefully as the TC becomes more in use, we will see more of the europe only spec items become available.
I'd be shocked if you needed to change the valves to run boost, not sure about natural gas though.
Lots of people have boosted Duratecs in the Focus with great success even with all stock internals.
I did a little looking and the old NGV Crown Vic and F-150 did list NGV specific valves but I kind of wonder if it was due to size rather than material because they listed completely different heads for them as well.
Check out FS Werks and the Forced induction section on Focaljet to see what people are doing with these engines.