Hey Paul,
The ring is an expander to increase compression as you'd assumed, it has no relation to a 4 stroke oil ring and has a different function.
80 os is a Hard size to get, ill make some enquiries, otherwise check the ODK online store, or post your enquiry here in the wanted forum.
If you have no luck, id just get another barrel and go from there...They are still around and You should find one up your way.
The 9 has no relevance and was probably the tech or re-borers mark.
