Spot on ZFT.
It was a "development" of the old 3 axis system, achieved by mounting the 3 axis motion onto a a pair of "linear bearings" - i.e. a sort of special "railway track" - to simulate Sway (e.g. for engine out at TO, etc). It was the "poor man's alternative" to a full 6 axis motion, (remember, the cost of that sim was MORE than the cost of a ready-to-fly F27 aircraft!), and as you say, the 4 axis never caught on.
AFAIK it was a Refdifon-only offering.
Yup, the grey (I prefer the colour "silver" actually, much more "interesting) is definitely rampant in (the small amount) of hair remaining!
Krgds
AES