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I realize that these are just small children, but even so, this horn looks massive!
Has anybody ever seen on of these in person or does anybody know any details
at all like specs? how many were made? what key? etc. (looks Bb to me).

Couesnon had a big fire in the late 70's and all their records were lost. The current owners don't seem to care about what was made in the past. Kind of sad.