Ian. The drive sleeve with the undercut is indeed the plunger version. Using a plunger nut with your S/A drive sleeve is fine in theory, but as you appreciate with the plunger design the slide moves from a splined to a plain section. While the ID of the drive sleeve splines and OD of the nut nose are the same, the internal splines on the S/A cush are shallower as shown, and will not bear onto the plain nose of the Plunger nut. The S/A slider is also of less depth than the Plunger in comparison and there may be a tendency for it to cant over and jam at full lift.
As the plunger sleeve has already been ground down to take the S/A Sprocket, a complete plunger cush set up could be used, although the profiles of the cush ramps are a poor match. From your picture the Plunger Sleeve looks to offer enough lift, so should work with the rest of the bits. The poor depth of spline engagement is the stumbling block here, but is obviously enough to take the load as in the later design.
The reason for the small amount of lift using your "correct parts" still baffles me. Somewhere out there is there a S/A drive sleeve that pokes at least 8mm above your stacked sprocket and sliding sleeve? The last paragraph of the original post to this thread says it all.
Chain alignment is taken care of by shimming between the drive sleeve and oilseal spacer, as already mentioned and has no influence on the amount of available cush lift, affecting only the final position of the tightened nut on the crank.
Swarfy.
