(Pete) I'm preparing myself for negative e-mails on this one.

This was one of the "Mystery Horns" in Helen's old 4Images gallery. Let me chop down the commentary and give you some reasons why I picked SML as the manufacturer:

* Keyguards are identical to a couple different "Rev. A" horns.
* Rolled tone holes. That's kind of difficult to find on French-made horns.
* The neck brace is not standard on SML "Rev. A" horns.
* The "button" chromatic F# key is found on other "Rev. A" horns. Some had no chromatic F# at all.
* SML produced stencils for Jen-Co Harmonia, although this is the first "Rev. A" I've seen.

Things I'm not quite sure of:

* G# key cluster. It does look close to other SMLs, but it has an odd "extension" for the low Bb.
* (Probably) altissimo Eb trill or altissimo F# key for the right hand. I don't recall seeing this on other SMLs.

The second best pick is Pierret. They made a bazillion models, but I can't recall one with rolled tone holes.

If you want to give me a second opinion, please do! I'm at pete-at-thesax.info.