Please find two new photos on the Photo Gallery under Steamchief. Thanks very much to those who followed up on my December postings and questions.
The missing link was provided by Conrad Milster. The previous uploaded photos had been taken in 1975 when the ship was being used as a barge. Mr Milster was kind enough to provide photographic evidence under operating conditions - and a description of the operation. The feedback loop missing in the photos was, in fact, a slip eccentric fitted on the paddlewheel controlling the valve mechanism by means of a horizontal eccentric rod shown in the uploaded photos. This apparently had been removed when the barge conversion took place.
A spring loaded handle on the rod allowed the slip eccentric to be unhooked. Manual operation of the valves - via the large vertical rod in the photographs - took over - very similar to beam engine practice. Once the valves had been manually set for the direction of travel, the eccentric rod could be "hooked" on to the mechanism just above the counterweight and the valve gear engaged.