Hi
Looks like the flywheel you have there is one for the debender boingy/110 engine. Just been out to my garage to measure them for you and.....the boingy/100 flywheel is the diameter you have - the series flywheels I have a a centimeter or so smaller in diameter. Also the ring gears are considerably different. The boingy/110 one is wider than the series one and appear to have slightly different spacings for the teeth (CBA to count them!)...and in addition, of course the boingy/110 engine uses a pre-engaged starter so the ring gear gets worn on the engine side, as aagainst the series which uses the inertia type starter which, therefore, get worn from the clutch/gearbox side.
There are other difference between the two types of flywheel too and they are not interchangeable (bolts, bronze bush etc) If you let me have an email address I can take a photo for you and send it.
HTH
Dave