My God! A response! Thank you! Actually, concerning the Decca International tonearms, I used to live in Europe and tried in all kinds of ways to get one of them. The company which is sitting on them - if they still have them - is Tjoeb Ah! They never answered any of my requests for information. Maybe they still have them. Though the arm is largely plastic, like the cartridge it is quite brilliant: it is a unipivot stabilized by magnets, with a bubble level in the headshell. If you can get one, then let me know.
As to the horizontal leveling question, I have to report a strange thing. Some time ago in my desperation, I acquired a Mayware tonearm to try with my cartridge. My Decca's diamond is actually glued crookedly onto the cantilever, and so does not hang straight down. The Mayware does not have any stabilisers of any sort, the counterweight does not hang below the pivot point, and so it is perfectly centred. Well damn me if the tonearm doesn't actually tilt precisely in response to the diamond's orientation, tilting just so so that the diamond points straight down! And it sounds perfectly centred and so on and stays stable without wobbling, giving the perfect imaging only a Decca can give (mine is a Super Gold with VdH stylus). Here is an unexpected "pro" in response to all the "cons" the Mayware is accused of. Of course, if the Mayware had the outriggers and the low-slung counterweight everyone makes such a fuss over, then my Decca wouldn't work. Hmmm...
Another 'table which works well with the Decca is an early Maplenoll air-bearing 'table with fluid damping trough. The headshell is held with a hex-nut, and so can be tilted to the required degree with the use of a small mirror to observe the diamond. After a helluva lot of wheeling and dealing, I have recently re-acquired this particular Maplenoll, which, by the way, is considered a Class A or B 'table by the incomparable Salvatore, though I have no idea if he is trustworthy (but he seems to be on the ball). The linear-tracking Maplenoll tonearm plus Decca gives the best imaging it is possible to have, with the added bonus of all the usual Decca attributes. But the Decca is noisy and will hum in some circumstances (I am still fiddling with the Maplenoll, and will report on this if there is interest), and so I keep a variety of MMs and MCs and 'tables around, "for I sip analogue rigs like wine," as there is no perfection in this world.