Justcurious,
The large ring Brno pre-war sporter that I saw here also had the brass plate around the stock wedge exactly as pictured. There would be a need to re-enforce the wood around the wedge hole, so I am thinking it was indeed a factory feature.

Your Peruvian small ring is very similar to the G33/40 except that it also lacks the profile of the left rail which actually makes it look like a large ring action:

John