I'd tend to think that if it was done in the field then by a skilled armorer, what furthermore means that the screw heads would not be as damaged as on the sample in Storz book. It cannot be outruled that they were replacements in the field, on the other hand it is much more likely that someone used another elevation ring as donor.
Don't get me wrong, your scope nevertheless is very rare and in nice condition. It is a great piece to own, and maybe one day you find another opposite mixed scope and you can swap back the elevation rings.