Saxophone repairman Matt Stohrer of http://www.StohrerMusic.com goes out on a limb and talks about a horn that he has only seen four of in his entire life- but given that it is unlikely he will see many more, the philosophical maxim of «grip it and rip it» is applied.
Disclaimer: Take all this with a grain of salt. Information on these horns is hard to come by and often contradictory, and I am by no means an expert on these saxophones, though I have probably seen more than most- but not all- repairmen.
TONS of photos of this saxophone here: http://www.getasax.com/product_info.php?cPath=21_28&products_id=677
Link to more info on the Leblanc Semi-Rationnel, which oddly enough is one of the other ones I have worked one (its easy to remember serial number 9): http://bassic-sax.info/blog/?p=31687
Another link, mostly about the Leblanc System which is a derivative of the Rationnel: http://www.saxgourmet.com/leblanc.htm
A link about the Rationnel, Semi-Rationnel, and Leblanc System with LOTS of further links: http://thesax.info/blog/le-rationnel-semi-rationnel-srb-and-leblanc-system-draft/