Chris,
As the crankshaft taper only measures 25mm I am pretty sure that the whole of your engine is either OB or OC (but with a DT airbox grafted on). From the photos you posted last year, it looks as if the clutch linings are rivetted to the flywheel backplate, so presumably your clutch has a one sided driveplate - in which case, lifting the clutch just moves the driveplate away from the backplate. This is the same setup as used on the sidevalve models of the same era. The loose ring shown in your previous photos is one half of the thrust bearing - this should fit over the boss of the flywheel and bear against the face of the clutch sprocket - and there should be a matching half that fits into the clutch release cam. Between these 2 halves there should be a bronze ring with trapped ball bearings - this completes the thrust bearing assembly. When the whole clutch is fully assembled, there should be some free play on the clutch release lever - if there isn't, the thrust bearing will be under permanent load, and will fail prematurely. Likewise, when the cable is fitted, it should be adjusted so that there is about 1/8" of free movement.
If you are attempting to re-manufacture the tracks for the thrust bearing, they should be made out of good quality case hardening steel. Ideally they need to end up being glass hard on the surface but with a tougher core to withstand the loads that will be applied.
Regards,
Eddie.