I don't know whether this solves the anomaly or not, but John Michell gave me one of these arms many years ago, along with an SME mounting plate for my GyroDec. The reason for an SME armboard is the fore-and-aft (or, more properly, I suppose, diagonal) adjustment; if the armboard has an oval hole (not a round one as shown) with overhang adjustment screw (7 on the illustration) there's a good 5mm of adjustment possible. (If you can't drill an oval cutout, as per an SME 3009 armboard, the hole should really be 35/36mm diameter. The base plate is sufficient diameter to fully cover it.)
I never actually got around to trying it out properly, since one channel turned out to be dead: I've finally got around to looking at it, and rather mysteriously, the core of one arm lead appears to have somehow either dissolved or vanished. So I'm in the process of plucking up courage to solder up a replacement.
I imagine most of these arms that may be still around have long lost the disc the set-up instructions mention for adjusting the stylus overhang (which wouldn't be possible, of course, with a 32mm diameter hole in the armboard!); if anyone is interested—or would like to make one— it was an aluminium disc 5mm thick and 35mm diameter with a central hole drilled for the turntable spindle.
You can get the silicon damping fluid from Michell dealers. Or probably direct from Borehamwood if you ask nicely?