You lucky so-and-so...
I learned ("learnt"?) to play clarinet on a Buffet A bass clarinet with the Albert key work, a relic of my grandfather's music career in both Bavaria (where he was an officer with the Bavarian Army who dabbled in opera on the side) and here in the United States.
The A horn was the only one of his instruments remaining during the days of my youth. When he arrived here post The Great War, it was among the few high-value possessions that he and my grandmother were able to evacuate following the "red revolution" post war.
(Incidentally, its not generally known that old Unca Adolph Hitler, Mr. NAZI party later in his life, was a member of the left-wing elements that briefly controlled Bavaria post war. He did a pretty good job of covering this up (including imprisonment and killing of the witnesses to same), but it's all written down.)
When my grandparents arrived in generally pro-German Saint Louis, his engineering experience quickly saw him rise in the Fire Department, where he was able to make station chief before forced into retirement by injuries to his lungs following the "great" bleach factory fire. They then sold all of his new horn, since his lungs were short.
However, working as a civil servant, even as a "desk official" in the battalion, was not a route to the kind of money that he needed to raise ten or eleven children, so he immediately started playing music for money. No real opera here in the US (the Municipal Opera (musical theater) was the closest he ever got there), but tons of work in movie theaters and hotel orchestras that fit well with his work schedule with the battalion.
When he got over here, he immediately went to pawn his European horns (along with Grandma's jewelry) in order to raise some interim capital. But, every pawn shop he approached would take the A and Bb sopranos (both Buffet horns, from what I have seen of the supporting documentation) and the Bb bass, but none would touch the A bass. So, into a succession of closets it went until it was time to take little Terry off of stringed instruments (to this day, I continue to hate the feel of a viola under my chin) and onto a horn.
While the Albert "system" is a bit on the obsolete side, you can still play them as well as your skills can allow. And, starting on the relatively small Buffet A bass to low E, it was relatively easy to handle for my burgeoning sixth grade arms and neck.
All the tools you need are available in the Rubank series of clarinet methods. The Elementary volume comes with two fingering charts - a Boehm one (using a skeletal metal instrument at the one side, and an Albert one with a normal looking soprano horn. The lip technique on the bass is a bit more involved, but other than that it's a doddle.
I took a grand total of three lessons with a guy at the local Nottleman's music store, but he moved on to another shop on the far north side and that was that. Everything else I picked up on my own, including the talents needed to make the A to Bb transposition, and the need to drive the alto clef out of my head.
In doing so, I unwittingly adopted a technique common with baritone horn players over in Europe, who made the transposition from the bass clef parts in to the pitch of the baritone by learning to read the part with different names assigned to the notes. So, instead of reading the Eb as Eb, you just read it as low E.
A bit hard to express, but it was good enough to get me by for a couple of years. My school district's music supervisor loved having the clarinet parts in the simple stuff we played doubled at the octave, and he encouraged me in my efforts (indeed, he is supportive to this day).)
However, as my technique developed, the district urged my parents to get me a Boehm system instrument. As the Boehm bass horns were too expensive, and as the same guy who got me started on the clarinet offered a one for one trade for a mid-level Boehm horn, my skinflint mother jumped at the chance and thus I became a "real clarinet player".
As I rose through the education system, I gradually accumulated the proper outfit for the orchestras and bands that I played in (a pair of Selmer Bb and A horns, and a bass (Boehm, of course) in Bb bought for my exclusive use by the district (a Bundy, mind you, but one with a floor peg). I also started playing sax, and picked up enough bassoon to get by on a show book or second chair in orchestra. However, I always missed the "sweet" sound and feel of my Albert bass.
Fast forward to college at a pathetic little pile down in Springfield MO (Drury College), where the bass that I was using was one of those pathetic Kohler horns, with a damaged register key, a crack in the lower joint and no peg. However, one fine day I was rummaging around in the school's horn room, looking for a working baritone (I found one, although not in working condition), when I blundered into a "pouchet" style case stuffed into the back of the storage.
From the size and the style, it looked like a duplicate of my old Albert bass. However, his time it was Buffet bass clarinet in Bb. Color me happy as hell.
The instrument was a total mess, with all of the pads eaten away by bugs, and the key work smelly and corroded. But a week's worth of work with lighter fluid and bore oil, penetrating oil, key oil and small screwdrivers, I got it cleaned up enough to take it up to Saint Louis and have the re-padding and regulation done.
While the bell and neck on that horn can't compare to those on your horn (no shine left at all, anywhere on the instrument, and also no lyre mount on the neck like the one in your photos), when fixed up I had a bass (albeit one that only descended to low E) without compare. I had to buy another Rubank Elementary method (for the fingering chart), but the system came back in less than a week.
When I left the hell that was Springfield, I approached the god-like Dr. Don Verne Joseph, the head of the music department, and offered to buy the horn from the school (since few others were playing the Albert system - none in fact with the local collegian community, many of whom tried the horn and loved the tone, but couldn't get their Boehm oriented heads around it). His answer was an immediate and resounding "No!"
(Despite his lofty status, the only thing that DVJ was into in a big way was the college "laboratory jazz ensemble". So much Basie was played that you could have floated a boat in it. Stuck up snob...)
I've since been back and inquired after the horn a second time, but it had disappeared without a trace. Upon reflection, I probably could have walked off with the thing, but that damn'd ethical conscience kept me from doing so. On top of this, none of the freshman level base courses (literature/composition, and "civilization" something or other) would transfer to a real school. So, I started my sophomore year as a half-sophomore - thanks a lot, Drury!
I've bought a couple of Albert basses since (both of Italian production, and more stiff and unresponsive instruments you will never play, I assure you). I've kept my eyes open back when I could still play a horn, but never saw a Buffet Albert bass on offer.
When playing clarinet, I prefer the Albert and Oehler systems in sharp-rich environments (orchestral and shows, along with big band stuff) and the Boehm instrument for the military band stuff
As for playability, there are some intonation issues with the Albert instruments (both soprano and bass - I trust that you didn't spend your money on a high pitch horn), but you learn to deal with them in time. In particular, the notes produced by the first finger down on the lower joint seemed to be a trifle sharp - I've been told that this may have been an artifact of the different notes being emitted - um - "differently".
The differences with the first fingers take some getting used to, but if you can manage a sax, you won't have much difficulty. A Selmer mouthpiece from their standard lineup fits the neck just fine, at least on the two that I had experience with. (I found the C** to be the best.)
For a case, you will probably have to go custom. I tried my Buffet from Drury in the wrong case once - I had it and the Kohler out at an orchestra rehearsal, and put it away in the Kohler case by mistake whilst distracted by an attractive 'cello player) and the two joints simply did not fit the Boehm horn case layout.
That manual register key is a little hard to master at first, but after a while you even learn to 'half hole' the second register when you trip it as you progress up the horn - it eases the production of the lower most tones in the clarinet register.
If I could still blow a horn, I'd probably come by and steal it from you. Since I can't, all I can offer is congratulations on an excellent find. Besides, I've got Pete's matched pair of Selmer A and Bb metal full Boehm horns ahead of you on the list.