I was partly involved in some research on contra-rotating props in the 80s, mainly looking at the acoustics and aerodynamics.
The only examples we could get for flight testing were the Fairey Gannet and the Avro Shackleton.
The Gannet had twin Mamba engines driving into a co-axial hub arrangement, and the propellers could be varied in pitch and RPM independantly of each other. If one engine failed you simply stopped and feathered its propeller.
The Shackleton I believe uses a planetary gear arrangement between the Griffin engine and the propeller and the propellers are geared to rotate at the same speed in opposite directions.
Unfortunately I didn't take any interest at the time in the transmission arrangements, but I hope this is of some use.