You might want to contact this ClubCobra member, who is actually using 2 of the inline 4V's on a former, modified, 6x2 intake:
ClubCobra posting
As for whether I've seen them, no.
As I understand it, they have no idle-circuitry, and so, aren't too practical for street use. They were designed as a way around restrictions on 2x4 setups in racing and so are pretty much race-oriented. I believe they were available from Ford, for the small blocks mainly though. They came in two sizes, both of which were probably too small for their intended engines' level of performance.
The engine shown above with the inline 4V was a race piece. The block was filled and it had something like 14:1 compression if I remember right. It was being offered for sale by Ron Miller of FPP for a gentleman in New York (again, if memory serves).
They're cool as a part of history, on a day-to-day usage basis though, I think there are better setups available, then and now. As I said, they were just created as a loophole around a rule in the day.
On another subject, in this month's Popular Science, there's a pretty in-depth article about the development of the new Ford GT(40).