Hi Graham,
The markings on the clutch are obviously a previous owners attempt at accurately setting the valve and ignition timing. The large markings are at 10 degree intervals, with smaller markings at 2½ degree intervals.
Regarding the plate in the timing chest - the only purpose I can think of, is that it may have been fitted as a baffle to deflect oil spray if an auxiliary breather had been fitted to the oil filler plug.
Regards,
Eddie.