Took me a while to find it again, but I can't seem to link the photo. If you'll go to "Xack"s profile on here though, you can see a photo of his West Coast with the Cobra Classic CS seats he's using in his build.
So there's the Classic CS at 18.9" width:
Classic CS - Historic - Cobra Seats
The Classic RS at 19.3" width:
Classic RS - Historic - Cobra Seats
The Clubman, which allegedly somehow worked at 19.69" width:
Clubman - Sports - Cobra Seats
...and those Mazda seats IndyCobra cited in the Lone Stars look right at home in the Cobra too.
Still looking for a pic of a Navigator seat in one...
This seems to be a common discussion amongst cobra owners though, so maybe we could ultimately get a fairly comprehensive list of seats that work well in Cobras out of this thread and sticky note it?