EDIT : Ack, sorry folks....what an auspicious start for me on this site :0.....I misread the pics in post 7 as being of this horn in question; in fact, it was Milandro posting pics of a Hammerschmidt.
So I more or less retract my prior attribution.
But I am going to chime in here with some (updated) observations, here, as David UK directed me to this discussion.
Some observations:
look at the escutcheons (i.e. 'feet') of the posts on the subject saxophone. They are round shape.
So, a matching suspect would likely have round feet.
Next, the G# trill key is an OLD detail....I have these before....on a very old Holton or two, from the 20's. So, this horn has a number of details of a pre-1940;s instrument....
I look at post feet, I look at ferrules, I look at key touches, octave mechanisms, and the fin armature of the F# keycup which closes the G# keycup. Then the octave mechanism. For me, these are more defining features than, say....keyguards and bell braces and such .....
But my issue with the Guenot attribution is they do not have compatible details in many aspects. The Guenot has oval post feet, some posts are ganged onto a single foot (spat keys), there is also some ribbed construction; the G key is detached from the upper stack rod and has a pair of arms extending to the octave mech (while the suspect has a G key attached to the upper stack rods and a single armature to the octave mechs). Back to the spats, the ganged posts there are the result of Guenots (the ebay one and Helen's bass sax one) having a separate barrel for each spat key, while the suspect horn has a single rod connecting both keys. Unfortunately, the Guenot tenor has no front F, because that would have helped considerably in puzzling this out.
The problem with a comparison of A (suspect) to B (Guenot) is that they do not seem to be similar era horns, the suspect being around 10 years older or more.....which makes things harder to figure, since a maker could have changed their engineering at some point....