Neil,
In the top photo, the clutch operating arm has a hardened thrust ring let into it. The cage with balls presses against it - then there should be another thrust ring to complete the thrust bearing assembly - I think the soft steel washer has at some time been used in lieu of a hardened washer - also, looking at the fifth photo, it looks as if the bearing has run direct against the end of the hub of the pressure plate at some time - the wear looks deep enough for the bearing cage to have rubbed on the end of the hub - maybe, the soft washer was inserted to gain some clearance. Also in photo 5, the odd wear patches on the pressure plate give the impression that the pressure plate may be distorted and will need some careful attention to get it running true again.
When the clutch plate is slid onto the pressure plate, the hub of the pressure plate should protrude further than the hub of the clutch plate - then when the thrust bearing lifts the pressure plate, the clutch plate will be free to spin.
Something else that may need investigation is the clutch linings - they look to be new, so are they the correct thickness? Do a dummy build of the flywheel assy - put the pressure plate and clutch plate into the flywheel and screw on the backplate without any spacer washers - the pressure plate/clutch plate should still be free to move about a 1/16" (so that the pressure plate can lift and free the clutch plate). Once you have established that the flywheel assembly is built correctly, you will probably have to re-shim the release assembly to get the orientation of the operating lever correct - this will likely be a trial and error job.
As Doug has said - there is something odd about your clutch/flywheel - normally, the smaller capacity engines didn't have the drive pins through the flywheel - that type of clutch was only fitted to the larger capacity OHV machines, so your clutch has probably been 'owner modified' at some time.
Regards,
Eddie.