I've watched an old video/French TV program of 1955 presenting a book written by Marcel Perrin, sax teacher at the Paris Conservatory. In the program, he speaks about the range of the sax and has a Couesnon keyed from low A to hi G.Chris J said:saintsday - Awesome collection!
My comment was more a thought aloud in that I thought keying to high G was quite a recent thing and had never heard of a vintage (if 40 + years can be called vintage) instrument with that. But if a modification, it looks like a factory modification from the pictures (though "squeezed in" puts it mildly!)
If I find the link again, I'll post it.
Please note also Jazzbrass' other Couesnon, Serial No. 2078, keyed to hi F#....
which in my view makes Couesnon an avant-garde sax manufacturer re. high keys (or low A for that matter).
My guess is that Jazzbrass' Couesnon with hi G was custom made for some pro player. A cool find.
Now, if someone knows the whereabouts of Perrin's alto, please PM me!!!