Think I'm sorted now. I found Draganfly's diagram wasn't, unusually, much help this time. The S/A BSA leaflet proved better, albeit with a different gear change mechanism. As Swarfy said, I was getting confused by the snap ring retaining the gear. Semantics, I suppose.
As far as I can see now, there's no thrust washer on the laygear's end, but one between the two last gears. Presumably this washer was available in different thicknesses to adjust end play.