I do not like much "deVille", is looks strange and previously I remember that we renamed all the "deVille" to "DeVille" because someone else (MrCadillac?) told us it was not correct
"DeVille" seemed the better choice to me, but if you think that "deVille" fits better (e.g. if it is more used than the other variants) I have no problem.

The "Convertible" in model name should be used if the car was named that way in the commercial documents. If they didn't use the name "DeVille Convertible" in that way then we should just put it as extra info.