OK. I've beaten myself up for about 1/2 hour on this horn, so I'm letting y'all take a crack.
The horn. It's engraved "Atlantic."
* My opinion is that this horn is extremely close to some of the Max Keilwerth horns, however that chromatic F# is wrong. There's also another thing I'll get to in a minute.
* I thought it looked a lot like a very early -- like Modell 1 -- Julius Keilwerths, but there's that thing I'll get to in a minute.
That bell-to-body brace = Germanic, tho.
I looked at a variety of other horns and rejected many makes and models immediately. Some would have the same bell-to-body brace, but wouldn't have the chromatic F# or the G# table would be wrong. There's also the bracing of the key arm on the bell keys and that's very distinctive.
I did some Googling and found that there's another similar Atllantic out there. Linky. (Even 6 years later, the links still work.)
If you have a chance to go through the pics in that thread, you'll find an almost identical horn to the one I posted, but the neck is different. But, because the body is almost identical, I can tell you that there's no "Best in the World, JGK" or "Pure-Tone" stamp, so bye-bye Max or Julius Keilwerth. 5-digit serial number shoots down Kohlert -- and pre-WWII Kohlerts looked different, anyway.
Lillelobo (the poster in the thread I mention) does point out that I had an Amati on saxpics.com that looks similar, but the only points of similarity to Lillelobo's horn are the neck and the chromatic F# key, everything else is different and, as noted, the neck on the horn I have on thesax.info looks very different.
The last thing is that I have a Buescher Atlantic archived somewhere, which I'll try to find (they weren't great pics, anyway). I mentioned, awhile back, about a couple other Not Buescher-Bueschers, too. Interesting ....