G'day

Some information that covers your question:

I had a BC-348 mount with no connector and used the Russian connector to complement it and install my BC-348. It is not a fit without modifying thr Russian connector, it need minor mechanical corrections to properyl fit. However it was not difficult and it worked. Not having a complete Russian mount I can unfortunately no say anything about fitting the BC-348 once the connector is adapted.

Hope this helps a bit. 73, Ulrich  hb9aik - vk2ani