Tim,
The arrangement described by Eddie is slightly later than the EW, the rollers were introduced with the S6 models or certainly had appeared by then. The EW use solid pins, slightly smaller than the subsequent rollers. 5/16 inch if I remember correctly, but same diameter as the fine thread through the ring which you located. The pins have domed ends and thread through the ring and into those dimples in the aluminum hub that you noted. That stops the ring from slipping around. The other end has a screw driver slot to drive them home.
The solid pins tend to develop flats rather quickly. This does not seem to impede the action at all on the throw out cam ramps, but it does quickly add slack to the clutch cable.
When they first went to the rollers, the ring only had one groove. Presumably they adjusted the location of the ring and then drilled and tapped for the stop pin. Later they added a sequence of grooves to allow adjustment, or more flexibility at the factory for initial setting if the stop pin was installed in advance. I suspect the latter as the clutch linings wear slowly so once the problem of flats on the solid pins were eliminated the need for gross adjustments with the ring ex-factory was mostly eliminated. Unless one is swapping parts about from various sources.
This is the solid pin type. This is a 600EW, but it is the same for the 350EW, right down to the part numbers.
This is the roller style described by Eddie, with examples of one, three and four adjustment grooves:
-Doug
