After playing with the 6" Darlot some more this weekend, I stumbled across this website :-
http://www.lungov.com/wagner/c/090c.html
What is interesting is the history of the original Darlot Cone Centraliseur variant. Apparently, if you remove the front element and place the rear group in it's place reversed, you get a landscape lens hence the phrase Vis Paysage for landscape, and Vis portrait for portrait written on some of them. Similarly, the front element can go into the back reversed and becomes a portrait lens!!!
As a test, I did the swap with my Darlot 6" and was very suprised it actually works on my lantern lens. You need a lot of bellows extension, but it covers 4x5 really easily (no vignetting) with no really swirly fall off, but more of a creamy/dreamy bokeh. Could be a nice pictorial option for when swirlies are not desired!!! Like I said, it takes quite a bit of bellows, but my Chamonix handled it okay. I am not sure of the effective focal length, but it was nearly at full draw even at infinity. Just thought I'd share.
These things continue to surprise me!!